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Sleep paralysis is a condition characterized by paralysis of the body shortly after waking up (known as hypnopompic paralysis) or, less often, shortly before falling asleep (known as hypnagogic paralysis). Physiologically, it is closely related to the normal paralysis that occurs during REM sleep, also known as REM atonia.
Sleep paralysis occurs when the brain is awakened from an REM state into essentially a normal fully awake state, but the bodily paralysis is still occurring. This causes the person to be fully aware, but unable to move. In addition, this state is usually accompanied by certain specific kinds of hallucinations. This state usually lasts no more than two minutes before a person is able to either return to full REM sleep or to become fully awake, though the sense of how much time has gone by is often distorted during sleep paralysis. People who are fortunate enough to be facing a clock while having an episode may often be surprised to see how little time has gone by during an episode that seems to last a very long time.
More often than not, sleep paralysis is believed by the person affected by it to be no more than a dream. This is the reason why there are many dream recountings which describe the person lying frozen and unable to move. The hallucinatory element to sleep paralysis makes it even more likely that someone will interpret the experience as simply a dream, as one might see completely fanciful objects in a room alongside the normal vision one can see.
Many report hallucinations during episodes of sleep paralysis. The features of these hallucinations generally vary by individual, but some are more common to the experience than others:
- Sensing a "presence" (often malevolent)
- Pressure/weight on body (especially the chest). See for example the painting in the beginning of this article.
- A sensation of not being able to breathe or move
- Impending sense of doom/death
- Auditory hallucinations (often footsteps or indistinct voices, or pulsing noises). Auditory hallucinations which are described as noise instead of hallucinations of legible sounds, are often described to be similar to auditory hallucinations caused by Nitrous Oxide by persons who have experienced both.
- Visual hallucinations such as lights, people or shadows walking around the room
- Floating sensation (sometimes associated with out-of-body experiences)
- Seemingly seamless transition into full hallucinations or dreaming, also associated with out-of-body experiences
- Tactile hallucinations (such as a hand touching or grabbing)
- Falling sensation
- Involuntary movements (sometimes the feeling of sliding off of the bed or even up walls).
Little is known about the physiology of sleep paralysis. However, some have suggested that it may be linked to post-synaptic inhibition of motor neurons in the pons region of the brain. In particular, low levels of melatonin may stop the depolarisation current in the nerves, which prevents the stimulation of the muscles.
There is also a significant positive correlation between those experiencing this disorder frequently and those suffering from narcolepsy. However, various studies suggest that many or most people will experience sleep paralysis at least once or twice in their lives.
Some report that various factors increase the likelihood of both paralysis and hallucinations. These include:
- Sleeping in a supine position (facing upwards)
- Irregular sleeping schedules; naps, sleeping in, sleep deprivation
- Increased stress
- Sudden environmental/lifestyle changes
- A lucid dream that immediately precedes the episode
- In India, there are two thoughts about sleep paralysis. One of the signs of approaching enlightenment is "witnessing sleep," that is to say, being seemingly lucid in sleep — such as with sleep paralysis. It was also believed within the movement that rakshasas (Hindu demons) may assail those making strides towards their own enlightenment and the good of all mankind. The other thought is a female entity, called Mohini (a demoness from the underworld), comes into the night-time world by means of ascending through a deep well. She is enchantingly beautiful, yet simultaneously horrific, unearthly, and deadly. Like her British Isles counterparts, she also seeks a male lover and human genetic material, presumably for the purpose of bearing a hybrid demon/human child.
- In Japan, sleep paralysis is referred to as kanashibari (金縛り, literally: "bound or fastened in metal": kana: metal, shibaru: to bind, tie, fasten")
- In Newfoundland, as a visit from the "old hag" (Ag Rog)
- In Mexico, as subida del muerto (the dead getting on top)
- In Turkish, as karabasan (black buster) and in Hazaragi, as Syahi Zer Kado (pressing ink)
- In the Southern United States, people have described it as "The witch riding your back"
- In Korea, it is referred as Gawinullim, literally in english: "To be pressed by Gawi." The meaning of Gawi is unclear but generally known to mean "spirits" or "demons." The word "Gawi" in Korean is a homonym which also means "scissors," which creates confusion for the accurate meaning of the word.
- In Indonesia, Javanese peoples called it "nindih" (To be seated upon)
- In Philippines, Sleep paralysis is often associated with Bangungot.
- In Vietnam, sleep paralysis is known as "ma đè", meaning a ghost or spirit lying on top of or pressing down on the person.
- The common belief in China is that a spirit or ghost is sitting or lying on top of the individual while they were sleeping, causing the sleep paralysis. This is thought to be a minor body possession by the forces from the dead, and usually doesn't cause any harm to the victim.
- In medieval times of Europe, attacks of sufferers of sleep paralysis may have given rise to the belief in mara, incubi, succubi, other demons and witchcraft.
- In traditional Russian belief symptoms reminiscent of sleep paralysis were attributed to the anger of domovoi, the home spirit, punishing people for bad husbandship or betrayal.
- Some scientists believe that many supposed occurrences of alien abduction, out-of-body travel, and other seemingly paranormal events may actually be due to misinterpreting the sensory effects of sleep paralysis.
- Others have argued that sleep paralysis might be the point of separation of the "dream body" from the physical body and out-of-body travel then begins.
- Bower, Bruce (July 9, 2005). "Night of the Crusher". Science News.
- Sleep Paralysis Information Service
- Susan Blackmore on sleep paralysis
- The Skeptic's Dictionary entry on Sleep Paralysis
- Sleep paralysis at Here Be Dreams
- Sleep information and links from Stanford University
- Sleep Paralysis and Associated Hypnagogic and Hypnopompic Experiences from Waterloo University
- Abduction by Aliens or Sleep Paralysis? - Skeptical Inquirer magazine, May/June 1998de:Bewegungsunfähigkeit im Schlaf
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