Sleep paralysis
Sleep paralysis (also hypnagogia) is a sleep disorder in which the sufferer, about to fall asleep (the hypnagogic state) or upon just waking (the hypnopompic state), is unable to move, speak or otherwise cry out. Most people experience sleep paralysis once or twice in their lives. It is especially common in those suffering from narcolepsy. It is often reported as a terrifying state.
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Normal sleep paralysis
Normal sleep paralysis is thought to be due to mechanisms in the brain stem, particularly the reticular, vestibular, and oculomotor neurons, which prevent bodily movements, block sensory input and provide the forebrain with the internally generated activity that characterises brain activity during REM sleep. This is thought to be necessary to prevent the body from movements caused by dreams. Eyes however are not paralyzed by this system, and this exception was used to prove that lucid dreaming was an objectively verifiable phenomenon.
The disorder known as "sleep paralysis" occurs when the brain is awakened from a REM state into essentially a normal fully awake state, but with the bodily paralysis still occouring. 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 then two minutes before a person is able to either return to full REM sleep or to become fully awake.
Awareness during sleep paralysis
Accompanying hallucinations
Many report hallucinations during these episodes. The features of these hallucinations generally vary by individual, but some are more common to the experience than others:
Possible causes
Little is known about the physiology of awareness during 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
- Irregular sleeping schedules; naps, sleeping in
- Increased stress
- Sudden environmental/lifestyle changes
Cultural references
In Japan, awareness during sleep paralysis is referred to as kanashibari; in Canada, as a visit from the "old hag"; in Mexico, as subida del muerto (the dead getting on top). In medieval times, attacks of sufferers of sleep paralysis may have given rise to the belief in incubi, succubi and other demons.Henry Fuseli's painting The Nightmare is thought to be one of the classic depictions of awareness during sleep paralysis perceived as a demonic visitation.
The combination of paralysis and hallucinations has led some to speculate that sleep paralysis might be a cause of some alien abduction reports, out of body experiences and other paranormal experiences.
See also
External links