Taken from Wikipedia
Sleep paralysis is a condition characterized by temporary 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 (rapid
eye movement) sleep, also known as REM atonia. In that, some scientists and physicians
believe it to be a "natural" effect of the sleep cycle. Sleep paralysis occurs when the
brain is awakened from a 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 may be accompanied by hypnagogic hallucinations.
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.
Symptoms
The primary symptom of sleep paralysis is partial or complete skeletal muscle paralysis
during the hypnopompic or hypnagogic states. In other words, it is the sense of being aware
that one is unable to move or speak while falling asleep or waking up. Sleep paralysis may
also be accompanied by hypnagogic hallucinations. These hallucinations can be auditory,
tactile, and/or visual. If a olysomnograph is taken, at least one of the following will be
shown: skeletal muscle tone suppression, REM sleep at sleep onset, or dissociated REM sleep.
The sleep paralysis persists anywhere from a few seconds to a few minutes before the person
is able to either return to REM sleep or to become fully awake.
Possible causes
Sleep paralysis occurs during REM sleep in order to prevent the body from manifesting
movements made in the subject’s dreams. 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 depolarization current in the nerves, which prevents the stimulation of the
muscles, to prevent the body from enacting the dreamt activity (e.g. preventing a sleeper
from running when dreaming about running).
Many people who commonly enter sleep paralysis also suffer 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. Also conscious induction of sleep
paralysis is a common technique to enter a state of lucid dreams, also known as WILD .
* Artificial sleeping aids, ADD medications and/or antihistamines