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96-398: The night hag or old hag is the name given to a supernatural creature, commonly associated with the phenomenon of sleep paralysis . It is a phenomenon in which the sleeper feels the presence of a supernatural, malevolent being which immobilizes the person as if sitting on their chest or the foot of their bed. The word "night-mare" or " nightmare " was used to describe this phenomenon before

192-461: A fast Fourier transform of the TWF. The vibration spectrum provides important frequency information that can pinpoint the faulty component. The fundamentals of vibration analysis can be understood by studying the simple Mass-spring-damper model. Indeed, even a complex structure such as an automobile body can be modeled as a "summation" of simple mass–spring–damper models. The mass–spring–damper model

288-460: A "viscous" damper is added to the model this outputs a force that is proportional to the velocity of the mass. The damping is called viscous because it models the effects of a fluid within an object. The proportionality constant c is called the damping coefficient and has units of Force over velocity (lbf⋅s/in or N⋅s/m). Summing the forces on the mass results in the following ordinary differential equation: The solution to this equation depends on

384-430: A 1 Hz square wave . The Fourier transform of the square wave generates a frequency spectrum that presents the magnitude of the harmonics that make up the square wave (the phase is also generated, but is typically of less concern and therefore is often not plotted). The Fourier transform can also be used to analyze non- periodic functions such as transients (e.g. impulses) and random functions. The Fourier transform

480-471: A great struggle in a situation of paralysis. A similar folklore is present in the Sannio area, around the city of Benevento , where the witch is called Janara . In Southern Italy, sleep paralysis is usually explained with the presence of a sprite standing on the people's chest: if the person manages to catch the sprite (or steal his hat), in exchange for his freedom (or to have his hat back) he can reveal

576-503: A loss of muscle tone whilst in a dream-like state. For example, Maimie is asleep but calls out "What was that....It is coming nearer! It is feeling your bed with its horns-it is boring for [into] you", and when the Darling children were dreaming of flying, Barrie says "Nothing horrid was visible in the air, yet their progress had become slow and laboured, exactly as if they were pushing their way through hostile forces. Sometimes they hung in

672-424: A majority of the time. Though no large trials have taken place which focus on the treatment of sleep paralysis, several drugs have promise in case studies. Two trials of GHB for people with narcolepsy demonstrated reductions in sleep paralysis episodes. Pimavanserin has been proposed as a possible candidate for future studies in treating sleep paralysis. Some of the earliest work in treating sleep paralysis

768-433: A person is conscious but in a complete state of full-body paralysis . During an episode, the person may hallucinate (hear, feel, or see things that are not there), which often results in fear . Episodes generally last no more than a few minutes. It can recur multiple times or occur as a single episode. The condition may occur in those who are otherwise healthy or those with narcolepsy , or it may run in families as

864-459: A person or an animal which sits upon their chest. Despite the name, the attacker can be either male or female. Some suggested cures or preventions for the Old Hag include sleeping with a Bible under the pillow, calling the sleeper's name backwards or in an extreme example, sleeping with a shingle or board embedded with nails strapped to the chest. This object was called a Hag Board. The Old Hag

960-423: A random input. The periodic input can be a harmonic or a non-harmonic disturbance. Examples of these types of vibration include a washing machine shaking due to an imbalance, transportation vibration caused by an engine or uneven road, or the vibration of a building during an earthquake. For linear systems, the frequency of the steady-state vibration response resulting from the application of a periodic, harmonic input

1056-452: A real world environment, such as road inputs to a moving automobile. Most vibration testing is conducted in a 'single DUT axis' at a time, even though most real-world vibration occurs in various axes simultaneously. MIL-STD-810G, released in late 2008, Test Method 527, calls for multiple exciter testing. The vibration test fixture used to attach the DUT to the shaker table must be designed for

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1152-482: A result of continued helplessness, causing the subjects to struggle to end the SP episode. Sleep paralysis is mainly diagnosed via clinical interview and ruling out other potential sleep disorders that could account for the feelings of paralysis. Several measures are available to reliably diagnose or screen ( Munich Parasomnia Screening ) for recurrent isolated sleep paralysis. Episodes of sleep paralysis can occur in

1248-507: A result of specific genetic changes. The condition can be triggered by sleep deprivation , psychological stress , or abnormal sleep cycles . The underlying mechanism is believed to involve a dysfunction in REM sleep . Diagnosis is based on a person's description. Other conditions that can present similarly include narcolepsy, atonic seizure , and hypokalemic periodic paralysis . Treatment options for sleep paralysis have been poorly studied. It

1344-402: A swing and letting it go, or hitting a tuning fork and letting it ring. The mechanical system vibrates at one or more of its natural frequencies and damps down to motionlessness. Forced vibration is when a time-varying disturbance (load, displacement, velocity, or acceleration) is applied to a mechanical system. The disturbance can be a periodic and steady-state input, a transient input, or

1440-423: A system behaves under forced vibration. The behavior of the spring mass damper model varies with the addition of a harmonic force. A force of this type could, for example, be generated by a rotating imbalance. Summing the forces on the mass results in the following ordinary differential equation: The steady state solution of this problem can be written as: The result states that the mass will oscillate at

1536-418: Is overdamped . The value that the damping coefficient must reach for critical damping in the mass-spring-damper model is: To characterize the amount of damping in a system a ratio called the damping ratio (also known as damping factor and % critical damping) is used. This damping ratio is just a ratio of the actual damping over the amount of damping required to reach critical damping. The formula for

1632-644: Is a parasomnia resulting from dysfunctional overlap of the REM and waking stages of sleep. Polysomnographic studies found that individuals who experience sleep paralysis have shorter REM sleep latencies than normal along with shortened NREM and REM sleep cycles, and fragmentation of REM sleep. This study supports the observation that disturbance of regular sleeping patterns can precipitate an episode of sleep paralysis, because fragmentation of REM sleep commonly occurs when sleep patterns are disrupted and has now been seen in combination with sleep paralysis. Another major theory

1728-453: Is a mistake in the signaling pathway for arousal as suggested by the first theory presented, or whether the regulation of melatonin or the neural populations themselves have been disrupted. Several types of hallucinations have been linked to sleep paralysis: the belief that there is an intruder in the room, the feeling of a presence, and the sensation of floating. One common hallucination is the presence of an incubus . A neurological hypothesis

1824-442: Is a protective mechanism that differentiates between dangerous situations and determines whether the fear response is appropriate. The hyper-vigilance response can lead to the creation of endogenous stimuli that contribute to the perceived threat. A similar process may explain hallucinations, with slight variations, in which an evil presence is perceived by the subject to be attempting to suffocate them, either by pressing heavily on

1920-427: Is also believed that there may be a genetic component in the development of RISP, because there is a high concurrent incidence of sleep paralysis in monozygotic twins . Sleeping in the supine position has been found an especially prominent instigator of sleep paralysis. Sleeping in the supine position is believed to make the sleeper more vulnerable to episodes of sleep paralysis because in this sleeping position it

2016-460: Is an example of a simple harmonic oscillator . The mathematics used to describe its behavior is identical to other simple harmonic oscillators such as the RLC circuit . Note: This article does not include the step-by-step mathematical derivations, but focuses on major vibration analysis equations and concepts. Please refer to the references at the end of the article for detailed derivations. To start

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2112-869: Is believed to have played a role in the creation of stories about alien abduction and other paranormal events. The main symptom of sleep paralysis is being unable to move or speak during awakening. Imagined sounds such as humming , hissing , static , zapping and buzzing noises are reported during sleep paralysis. Other sounds such as voices , whispers and roars are also experienced. It has also been known that one may feel pressure on their chest and intense pain in their head during an episode. These symptoms are usually accompanied by intense emotions such as fear and panic . People also have sensations of being dragged out of bed or of flying, numbness , and feelings of electric tingles or vibrations running through their body. Sleep paralysis may include hallucinations, such as an intruding presence or dark figure in

2208-414: Is called resonance (subsequently the natural frequency of a system is often referred to as the resonant frequency). In rotor bearing systems any rotational speed that excites a resonant frequency is referred to as a critical speed . If resonance occurs in a mechanical system it can be very harmful – leading to eventual failure of the system. Consequently, one of the major reasons for vibration analysis

2304-402: Is defined as: Note: angular frequency ω (ω=2 π f ) with the units of radians per second is often used in equations because it simplifies the equations, but is normally converted to ordinary frequency (units of Hz or equivalently cycles per second) when stating the frequency of a system. If the mass and stiffness of the system is known, the formula above can determine the frequency at which

2400-428: Is defined by the following formula. [REDACTED] The plot of these functions, called "the frequency response of the system", presents one of the most important features in forced vibration. In a lightly damped system when the forcing frequency nears the natural frequency ( r ≈ 1 {\displaystyle r\approx 1} ) the amplitude of the vibration can get extremely high. This phenomenon

2496-455: Is equal to the frequency of the applied force or motion, with the response magnitude being dependent on the actual mechanical system. Damped vibration: When the energy of a vibrating system is gradually dissipated by friction and other resistances, the vibrations are said to be damped. The vibrations gradually reduce or change in frequency or intensity or cease and the system rests in its equilibrium position. An example of this type of vibration

2592-744: Is experienced equally in males and females. Lifetime prevalence rates derived from 35 aggregated studies indicate that approximately 8% of the general population, 28% of students, and 32% of psychiatric patients experience at least one episode of sleep paralysis at some point in their lives. Rates of recurrent sleep paralysis are not as well known, but 15–45% of those with a lifetime history of sleep paralysis may meet diagnostic criteria for Recurrent Isolated Sleep Paralysis. In surveys from Canada, China, England, Japan and Nigeria, 20% to 60% of individuals reported having experienced sleep paralysis at least once in their lifetime. In general, non-whites appear to experience sleep paralysis at higher rates than whites, but

2688-469: Is hurtful, but nothing is more productive of this disease than drinking bad wine. Of eatables those which are most prejudicial are all fat and greasy meats and pastry... Moderate exercise contributes in a superior degree to promote the digestion of food and prevent flatulence; those, however, who are necessarily confined to a sedentary occupation, should particularly avoid applying themselves to study or bodily labor immediately after eating... Going to bed before

2784-465: Is known as "the ghost pushes you down," and entails the belief in dangerous visitations from deceased relatives. In Egypt , sleep paralysis is conceptualized as a terrifying jinn attack . In the different regions of Italy there are many examples of supernatural beings associated with sleep paralysis. In the regions of Marche and Abruzzo , it is referred to as a Pandafeche  [ it ] or pantafica  [ it ] attack;

2880-420: Is less than the undamped natural frequency, but for many practical cases the damping ratio is relatively small and hence the difference is negligible. Therefore, the damped and undamped description are often dropped when stating the natural frequency (e.g. with 0.1 damping ratio, the damped natural frequency is only 1% less than the undamped). The plots to the side present how 0.1 and 0.3 damping ratios effect how

2976-553: Is much easier for a stimulus to arouse the individual. The vestibular nuclei in particular has been identified as being closely related to dreaming during the REM stage of sleep. According to this hypothesis, vestibular-motor disorientation, unlike hallucinations, arise from completely endogenous sources of stimuli. If the effects of sleep "on" neural populations cannot be counteracted, characteristics of REM sleep are retained upon awakening. Common consequences of sleep paralysis include headaches, muscle pains or weakness or paranoia. As

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3072-414: Is now compressing the spring and in the process transferring the kinetic energy back to its potential. Thus oscillation of the spring amounts to the transferring back and forth of the kinetic energy into potential energy. In this simple model the mass continues to oscillate forever at the same magnitude—but in a real system, damping always dissipates the energy, eventually bringing the spring to rest. When

3168-410: Is often referred to as predictive maintenance (PdM). Most commonly VA is used to detect faults in rotating equipment (Fans, Motors, Pumps, and Gearboxes etc.) such as imbalance, misalignment, rolling element bearing faults and resonance conditions. VA can use the units of Displacement, Velocity and Acceleration displayed as a time waveform (TWF), but most commonly the spectrum is used, derived from

3264-523: Is possible for the soft palate to collapse and obstruct the airway. This is a possibility regardless of whether the individual has been diagnosed with sleep apnea or not. There may also be a greater rate of microarousals while sleeping in the supine position because there is a greater amount of pressure being exerted on the lungs by gravity. While many factors can increase the risk for ISP or RISP, they can be avoided with minor lifestyle changes. Medical treatment starts with education about sleep stages and

3360-443: Is recommended that people be reassured that the condition is common and generally not serious. Other efforts that may be tried include sleep hygiene , cognitive behavioral therapy , and antidepressants . Between 8% and 50% of people experience sleep paralysis at some point during their lives. About 5% of people have regular episodes. Males and females are affected equally. Sleep paralysis has been described throughout history. It

3456-443: Is that in sleep paralysis the cerebellum , which usually coordinates body movement and provides information on body position, experiences a brief myoclonic spike in brain activity inducing a floating sensation. The intruder and incubus hallucinations highly correlate with one another, and moderately correlated with the third hallucination, vestibular-motor disorientation, also known as out-of-body experiences , which differ from

3552-442: Is that the neural functions that regulate sleep are out of balance, causing different sleep states to overlap. In this case, cholinergic sleep "on" neural populations are hyperactivated and the serotonergic sleep "off" neural populations are under-activated. As a result, the cells capable of sending the signals that would allow for complete arousal from the sleep state, the serotonergic neural populations, have difficulty in overcoming

3648-463: Is the Fourier transform that takes a signal as a function of time ( time domain ) and breaks it down into its harmonic components as a function of frequency ( frequency domain ). For example, by applying a force to the mass–spring–damper model that repeats the following cycle – a force equal to 1  newton for 0.5 second and then no force for 0.5 second. This type of force has the shape of

3744-436: Is the vehicular suspension dampened by the shock absorber . Vibration testing is accomplished by introducing a forcing function into a structure, usually with some type of shaker. Alternately, a DUT (device under test) is attached to the "table" of a shaker. Vibration testing is performed to examine the response of a device under test (DUT) to a defined vibration environment. The measured response may be ability to function in

3840-401: Is the minimum potential energy state) and in the process accelerates the mass. At the point where the spring has reached its un-stretched state all the potential energy that we supplied by stretching it has been transformed into kinetic energy ( 1 2 m v 2 {\displaystyle {\tfrac {1}{2}}mv^{2}} ). The mass then begins to decelerate because it

3936-421: Is to predict when this type of resonance may occur and then to determine what steps to take to prevent it from occurring. As the amplitude plot shows, adding damping can significantly reduce the magnitude of the vibration. Also, the magnitude can be reduced if the natural frequency can be shifted away from the forcing frequency by changing the stiffness or mass of the system. If the system cannot be changed, perhaps

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4032-582: Is to put one's husband's hat near the pillow while sleeping. Mokthi or Makthi in Albanian means "Nightmare". In Bengali folklore , sleep paralysis is believed to be caused by a supernatural entity called Boba ( Bengali : বোবা , lit.   'dumb'). Boba attacks a person by strangling him when the person sleeps in a supine position . In Bengal , the phenomenon is called Bobay Dhora ( Bengali : বোবায় ধরা , lit.   'Struck by Boba '). Sleep paralysis among Cambodians

4128-546: Is well-enough known in the province to be a pop culture figure, appearing in films and plays as well as in crafted objects. Nigeria has myriad interpretations of the cause of sleep paralysis, due to numerous cultures and belief systems that exist there. Sleep paralysis is sometimes interpreted as space alien abduction in the United States . Various forms of magic and spiritual possession were also advanced as causes in literature. In nineteenth century Europe ,

4224-454: The jinn . Research has found that sleep paralysis is associated with great fear and fear of impending death in 50% of sufferers in Egypt. A study comparing rates and characteristics of sleep paralysis in Egypt and Denmark found that the phenomenon is three times more common in Egypt than Denmark. In Denmark, unlike Egypt, there are no elaborate supernatural beliefs about sleep paralysis, and

4320-630: The Ammuntadore is known as a creature that mounts on the people's chest during their sleep to give them nightmares, and that can change its shape according to the person's fears. In Northern Italy, specifically in the Tyrol area, the Trud is a witch that sits on the people's chest at night, making them unable to breathe; to chase her away, people should make the sign of the Cross , something that would need

4416-516: The Pandafeche usually refers to an evil witch , sometimes a ghostlike spirit or a terrifying catlike creature, that mounts on the chest of the victim and tries to harm him. The only way to avoid her is to keep a bag of sand or beans close to the bed, so that the witch will stop to count how many beans or sand-grains are inside it. A similar tradition is present in the Sardinian folklore, where

4512-676: The mare in the word nightmare . The word might be cognate to Greek Marōn (in the Odyssey ) and Sanskrit Māra . Although the core features of sleep paralysis (e.g., atonia, a clear sensorium, and frequent hallucinations) appear to be universal, the ways in which they are experienced vary according to time, place, and culture. Over 100 terms have been identified for these experiences. Some scientists have proposed sleep paralysis as an explanation for reports of paranormal and spiritual phenomena such as ghosts , alien visits, demons or demonic possession , alien abduction experiences,

4608-476: The near-death experience and shadow people can, in many cases, be attributed to sleep paralysis. The "real-life" horror film debuted at the Sundance Film Festival on January 26, 2015, and premiered in theatres on June 5, 2015. Vibration Vibration can be desirable: for example, the motion of a tuning fork , the reed in a woodwind instrument or harmonica , a mobile phone , or

4704-641: The night hag and shadow people haunting. According to some scientists, culture may be a major factor in shaping sleep paralysis. When sleep paralysis is interpreted through a particular cultural filter, it may take on greater salience. For example, if sleep paralysis is feared in a certain culture, this fear could lead to conditioned fear, and thus worsen the experience, in turn leading to higher rates. Consistent with this idea, high rates and long durations of immobility during sleep paralysis have been found in Egypt, where there are elaborate beliefs about sleep paralysis, involving malevolent spirit -like creatures,

4800-652: The DUT-side of a vibration fixture is kept at a specified acceleration. Other "response" points may experience higher vibration levels (resonance) or lower vibration level (anti-resonance or damping) than the control point(s). It is often desirable to achieve anti-resonance to keep a system from becoming too noisy, or to reduce strain on certain parts due to vibration modes caused by specific vibration frequencies. The most common types of vibration testing services conducted by vibration test labs are sinusoidal and random. Sine (one-frequency-at-a-time) tests are performed to survey

4896-497: The air until Peter had beaten on it with his fists." Barrie describes many parasomnias and neurological symptoms in his books and uses them to explore the nature of consciousness from an experiential point of view. The Nightmare is a 2015 documentary that discusses the causes of sleep paralysis as seen through extensive interviews with participants, and the experiences are re-enacted by professional actors. In synopsis, it proposes that such cultural phenomena as alien abduction ,

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4992-429: The airway, which is a symptom prevalent in sleep apnea patients. According to this account, the subjects attempt to breathe deeply and find themselves unable to do so, creating a sensation of resistance, which the threat-activated vigilance system interprets as an unearthly being sitting on their chest, threatening suffocation. The sensation of entrapment causes a feedback loop when the fear of suffocation increases as

5088-401: The amount of damping. If the damping is small enough, the system still vibrates—but eventually, over time, stops vibrating. This case is called underdamping, which is important in vibration analysis. If damping is increased just to the point where the system no longer oscillates, the system has reached the point of critical damping . If the damping is increased past critical damping, the system

5184-399: The axis under test) permitted to be exhibited by the vibration test fixture. Devices specifically designed to trace or record vibrations are called vibroscopes . Vibration analysis (VA), applied in an industrial or maintenance environment aims to reduce maintenance costs and equipment downtime by detecting equipment faults. VA is a key component of a condition monitoring (CM) program, and

5280-404: The chest or by strangulation. A neurological explanation holds that this results from a combination of the threat vigilance activation system and the muscle paralysis associated with sleep paralysis that removes voluntary control of breathing. Several features of REM breathing patterns exacerbate the feeling of suffocation. These include shallow rapid breathing, hypercapnia , and slight blockage of

5376-404: The chests of sleepers. In Old English the name for these beings was mare or mære (from a proto-Germanic *marōn , cf. Old Norse mara ), hence comes the mare part in nightmare . The word might be etymologically cognate to Greek Marōn (in the Odyssey ) and Sanskrit Māra . Sleep paralysis Sleep paralysis is a state, during waking up or falling asleep , in which

5472-652: The cone of a loudspeaker . In many cases, however, vibration is undesirable, wasting energy and creating unwanted sound . For example, the vibrational motions of engines , electric motors , or any mechanical device in operation are typically unwanted. Such vibrations could be caused by imbalances in the rotating parts, uneven friction , or the meshing of gear teeth. Careful designs usually minimize unwanted vibrations. The studies of sound and vibration are closely related (both fall under acoustics ). Sound, or pressure waves , are generated by vibrating structures (e.g. vocal cords ); these pressure waves can also induce

5568-609: The context of several medical conditions (e.g., narcolepsy, hypokalemia ). When episodes occur independent of these conditions or substance use, it is termed "isolated sleep paralysis" (ISP). When ISP episodes are more frequent and cause clinically significant distress or interference, it is classified as "recurrent isolated sleep paralysis" (RISP). Episodes of sleep paralysis, regardless of classification, are generally short (1–6 minutes), but longer episodes have been documented. It can be difficult to differentiate between cataplexy brought on by narcolepsy and true sleep paralysis, because

5664-458: The correlation with REM sleep suggests, the paralysis is not complete: use of EOG traces shows that eye movement is still possible during such episodes; however, the individual experiencing sleep paralysis is unable to speak. Research has found a genetic component in sleep paralysis. The characteristic fragmentation of REM sleep, hypnopompic , and hypnagogic hallucinations have a heritable component in other parasomnias, which lends credence to

5760-400: The damping ratio ( ζ {\displaystyle \zeta } ) of the mass-spring-damper model is: For example, metal structures (e.g., airplane fuselages, engine crankshafts) have damping factors less than 0.05, while automotive suspensions are in the range of 0.2–0.3. The solution to the underdamped system for the mass-spring-damper model is the following: The value of X ,

5856-441: The damping ratio, the quicker it damps to zero. The cosine function is the oscillating portion of the solution, but the frequency of the oscillations is different from the undamped case. The frequency in this case is called the "damped natural frequency", f d , {\displaystyle f_{\text{d}},} and is related to the undamped natural frequency by the following formula: The damped natural frequency

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5952-433: The designer can target a fixture design that is free of resonances in the test frequency range. This becomes more difficult as the DUT gets larger and as the test frequency increases. In these cases multi-point control strategies can mitigate some of the resonances that may be present in the future. Some vibration test methods limit the amount of crosstalk (movement of a response point in a mutually perpendicular direction to

6048-475: The energy added by the force. At this point, the system has reached its maximum amplitude and will continue to vibrate at this level as long as the force applied stays the same. If no damping exists, there is nothing to dissipate the energy and, theoretically, the motion will continue to grow into infinity. In a previous section only a simple harmonic force was applied to the model, but this can be extended considerably using two powerful mathematical tools. The first

6144-442: The experience is often interpreted as an odd physiological event, with overall shorter sleep paralysis episodes and fewer people (17%) fearing that they could die from it. The night hag is a generic name for a folkloric creature found in cultures around the world, and which is used to explain the phenomenon of sleep paralysis. A common description is that a person feels a presence of a supernatural malevolent being which immobilizes

6240-432: The force is always opposing the motion of the mass attached to it: The force generated by the mass is proportional to the acceleration of the mass as given by Newton's second law of motion : The sum of the forces on the mass then generates this ordinary differential equation :   m x ¨ + k x = 0. {\displaystyle \ m{\ddot {x}}+kx=0.} Assuming that

6336-423: The forcing frequency can be shifted (for example, changing the speed of the machine generating the force). The following are some other points in regards to the forced vibration shown in the frequency response plots. Resonance is simple to understand if the spring and mass are viewed as energy storage elements – with the mass storing kinetic energy and the spring storing potential energy. As discussed earlier, when

6432-407: The frequency range of the vibration test spectrum. It is difficult to design a vibration test fixture which duplicates the dynamic response (mechanical impedance) of the actual in-use mounting. For this reason, to ensure repeatability between vibration tests, vibration fixtures are designed to be resonance free within the test frequency range. Generally for smaller fixtures and lower frequency ranges,

6528-662: The hiding place of a rich treasure; this sprite has different names in different regions of Italy: Monaciello in Campania , Monachicchio in Basilicata , Laurieddhu or Scazzamurill in Apulia , Mazzmuredd in Molise . In Newfoundland , sleep paralysis is referred to as the Old Hag, and victims of a hagging are said to be hag-ridden upon awakening. Victims report being completely conscious, but unable to speak or move, and report

6624-404: The idea that sleep paralysis is also genetic. Twin studies have shown that if one twin of a monozygotic pair ( identical twins ) experiences sleep paralysis that other twin is very likely to experience it as well. The identification of a genetic component means that there is some sort of disruption of a function at the physiological level. Further studies must be conducted to determine whether there

6720-482: The inability to move muscles during REM sleep. People should be evaluated for narcolepsy if symptoms persist. The safest treatment for sleep paralysis is for people to adopt healthier sleeping habits. However, in more serious cases tricyclic antidepressants or selective serotonin reuptake inhibitors (SSRIs) may be used. Despite the fact that these treatments are prescribed there is currently no drug that has been found to completely interrupt episodes of sleep paralysis

6816-482: The individuals who have experienced sleep paralysis have sporadic episodes that occur once a month to once a year. Only 3% of individuals experiencing sleep paralysis that is not associated with a neuromuscular disorder have nightly episodes. The original definition of sleep paralysis was codified by Samuel Johnson in his A Dictionary of the English Language as nightmare , a term that evolved into

6912-400: The initial magnitude, and ϕ , {\displaystyle \phi ,} the phase shift , are determined by the amount the spring is stretched. The formulas for these values can be found in the references. The major points to note from the solution are the exponential term and the cosine function. The exponential term defines how quickly the system “damps” down – the larger

7008-410: The initiation of vibration begins by stretching the spring by the distance of A and releasing, the solution to the above equation that describes the motion of mass is: This solution says that it will oscillate with simple harmonic motion that has an amplitude of A and a frequency of f n . The number f n is called the undamped natural frequency . For the simple mass–spring system, f n

7104-483: The investigation of the mass–spring–damper assume the damping is negligible and that there is no external force applied to the mass (i.e. free vibration). The force applied to the mass by the spring is proportional to the amount the spring is stretched "x" (assuming the spring is already compressed due to the weight of the mass). The proportionality constant, k, is the stiffness of the spring and has units of force/distance (e.g. lbf/in or N/m). The negative sign indicates that

7200-421: The magnitude of the difference is rather small. Approximately 36% of the general population that experiences isolated sleep paralysis develop it between 25 and 44 years of age. Isolated sleep paralysis is commonly seen in patients that have been diagnosed with narcolepsy. Approximately 30–50% of people that have been diagnosed with narcolepsy have experienced sleep paralysis as an auxiliary symptom. A majority of

7296-424: The mass and spring have no external force acting on them they transfer energy back and forth at a rate equal to the natural frequency. In other words, to efficiently pump energy into both mass and spring requires that the energy source feed the energy in at a rate equal to the natural frequency. Applying a force to the mass and spring is similar to pushing a child on swing, a push is needed at the correct moment to make

7392-432: The modern definition. The term was first used and dubbed by British neurologist, S.A.K. Wilson in his 1928 dissertation, The Narcolepsies. Such sleep paralysis was widely considered the work of demons , and more specifically incubi , which were thought to sit on the chests of sleepers. In Old English the name for these beings was mare or mære (from a proto-Germanic *marōn , cf. Old Norse mara ), hence comes

7488-537: The more frequently it returns, the greater strength it acquires; the propensity to sleep at this time is almost irresistible. J. M. Barrie , the author of the Peter Pan stories, may have had sleep paralysis. He said of himself "In my early boyhood it was a sheet that tried to choke me in the night." He also described several incidents in the Peter Pan stories that indicate that he was familiar with an awareness of

7584-427: The natural frequency of the system. Vibrational motion could be understood in terms of conservation of energy . In the above example the spring has been extended by a value of x and therefore some potential energy ( 1 2 k x 2 {\displaystyle {\tfrac {1}{2}}kx^{2}} ) is stored in the spring. Once released, the spring tends to return to its un-stretched state (which

7680-434: The nature of sleep paralysis. Prevention techniques include ISP-specific sleep hygiene and the preparatory use of various relaxation techniques (e.g. diaphragmatic breathing, mindfulness, progressive muscle relaxation, meditation). Episode disruption techniques are first practiced in session and then applied during actual attacks. No controlled trial of CBT-ISP has yet been conducted to prove its effectiveness. Sleep paralysis

7776-526: The other two in not involving the threat-activated vigilance system. A hyper-vigilant state created in the midbrain may further contribute to hallucinations. More specifically, the emergency response is activated in the brain when individuals wake up paralyzed and feel vulnerable to attack. This helplessness can intensify the effects of the threat response well above the level typical of normal dreams, which could explain why such visions during sleep paralysis are so vivid. The threat-activated vigilance system

7872-471: The person as if standing on the chest. This phenomenon goes by many names. In Albanian folk beliefs , Mokthi is believed to be a male spirit with a golden fez hat who appears to women who are usually tired or suffering and stops them from moving. It is believed that if they can take his golden hat, he will grant them a wish, but then he will visit them frequently although he is harmless. There are talismans that can provide protection from Mokthi and one way

7968-421: The room. These are commonly known as sleep paralysis demons . It may also include suffocating or the individual feeling a sense of terror, accompanied by a feeling of pressure on one's chest and difficulty breathing . The pathophysiology of sleep paralysis has not been concretely identified, although there are several theories about its cause. The first of these stems from the understanding that sleep paralysis

8064-419: The same frequency, f , of the applied force, but with a phase shift ϕ . {\displaystyle \phi .} The amplitude of the vibration “X” is defined by the following formula. Where “r” is defined as the ratio of the harmonic force frequency over the undamped natural frequency of the mass–spring–damper model. The phase shift, ϕ , {\displaystyle \phi ,}

8160-452: The signals sent by the cells that keep the brain in the sleep state. During normal REM sleep, the threshold for a stimulus to cause arousal is greatly elevated. Under normal conditions, medial and vestibular nuclei , cortical , thalamic , and cerebellar centers coordinate things such as head and eye movement, and orientation in space. In individuals reporting sleep paralysis, there is almost no blocking of exogenous stimuli, which means it

8256-428: The structural response of the device under test (DUT). During the early history of vibration testing, vibration machine controllers were limited only to controlling sine motion so only sine testing was performed. Later, more sophisticated analog and then digital controllers were able to provide random control (all frequencies at once). A random (all frequencies at once) test is generally considered to more closely replicate

8352-415: The swing get higher and higher. As in the case of the swing, the force applied need not be high to get large motions, but must just add energy to the system. The damper, instead of storing energy, dissipates energy. Since the damping force is proportional to the velocity, the more the motion, the more the damper dissipates the energy. Therefore, there is a point when the energy dissipated by the damper equals

8448-446: The system vibrates once set in motion by an initial disturbance. Every vibrating system has one or more natural frequencies that it vibrates at once disturbed. This simple relation can be used to understand in general what happens to a more complex system once we add mass or stiffness. For example, the above formula explains why, when a car or truck is fully loaded, the suspension feels "softer" than unloaded—the mass has increased, reducing

8544-417: The system “rings” down over time. What is often done in practice is to experimentally measure the free vibration after an impact (for example by a hammer) and then determine the natural frequency of the system by measuring the rate of oscillation, as well as the damping ratio by measuring the rate of decay. The natural frequency and damping ratio are not only important in free vibration, but also characterize how

8640-519: The two phenomena are physically indistinguishable. The best way to differentiate between the two is to note when the attacks occur most often. Narcolepsy attacks are more common when the individual is falling asleep; ISP and RISP attacks are more common upon awakening. Similar conditions include: Several circumstances have been identified that are associated with an increased risk of sleep paralysis. These include insomnia , sleep deprivation , an erratic sleep schedule, stress , and physical fatigue. It

8736-406: The usual hour is a frequent cause of night-mare, as it either occasions the patient to sleep too long or to lie long awake in the night. Passing a whole night or part of a night without rest likewise gives birth to the disease, as it occasions the patient, on the succeeding night, to sleep too soundly. Indulging in sleep too late in the morning, is an almost certain method to bring on the paroxysm, and

8832-600: The vagaries of diet were thought to be responsible. For example, in Charles Dickens 's A Christmas Carol , Ebenezer Scrooge attributes the ghost he sees to "... an undigested bit of beef, a blot of mustard, a crumb of cheese, a fragment of an underdone potato..." In a similar vein, the Household Cyclopedia (1881) offers the following advice about nightmares: Great attention is to be paid to regularity and choice of diet. Intemperance of every kind

8928-525: The vibration environment, fatigue life, resonant frequencies or squeak and rattle sound output ( NVH ). Squeak and rattle testing is performed with a special type of quiet shaker that produces very low sound levels while under operation. For relatively low frequency forcing (typically less than 100 Hz), servohydraulic (electrohydraulic) shakers are used. For higher frequencies (typically 5 Hz to 2000 Hz), electrodynamic shakers are used. Generally, one or more "input" or "control" points located on

9024-412: The vibration of structures (e.g. ear drum ). Hence, attempts to reduce noise are often related to issues of vibration. Machining vibrations are common in the process of subtractive manufacturing . Free vibration or natural vibration occurs when a mechanical system is set in motion with an initial input and allowed to vibrate freely. Examples of this type of vibration are pulling a child back on

9120-451: The word received its modern, more general meaning. Various cultures have various names for this phenomenon and supernatural character. The original definition of sleep paralysis was codified by Samuel Johnson in his A Dictionary of the English Language as nightmare , a term that evolved into our modern definition. Such sleep paralysis was widely considered the work of demons , and more specifically incubi , which were thought to sit on

9216-617: Was done using a cognitive-behavior therapy called CA-CBT. The work focuses on psycho-education and modifying catastrophic cognitions about the sleep paralysis attack. This approach has previously been used to treat sleep paralysis in Egypt, although clinical trials are lacking. The first published psychosocial treatment for recurrent isolated sleep paralysis was cognitive-behavior therapy for isolated sleep paralysis (CBT-ISP). It begins with self-monitoring of symptoms, cognitive restructuring of maladaptive thoughts relevant to ISP (e.g., "the paralysis will be permanent"), and psychoeducation about

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