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 paralysis that occurs as a natural part of REM (rapid eye movement) sleep, which is known as REM atonia. Sleep paralysis occurs when the brain awakes from a REM state, but the bodily paralysis persists. This leaves the person fully aware, but unable to move. In addition, the state may be accompanied by hypnagogic hallucinations.
In Chinese folk culture, sleep paralysis is referred as literally: "Ghost press bed"The belief is that a spirit or ghost is sitting or lying on top of the sleeping individual, causing the sleep paralysis. This is thought to be a minor body possession by the forces from the dead which doesn't usually cause any harm to the victim.
In Japan, sleep paralysis is referred to as kanashibari literally "bound or fastened in metal," from kane "metal" and shibaru "to bind, to tie, to fasten"
In Thailand, this condition is said to be caused by a spirit or "pee um" which sits or lie atop of the victim causing him or her to be immobile. The spirit causes no harm to the victim and is said to only be playing pranks.
In Scandinavian mythology, sleep paralysis was caused by a Mara, or mare - a kind of malignant female wraith who can also cause nightmares. She appears as early as in the Norse Ynglinga saga, but the belief itself is probably even older. "Mara" is the Old Norse, Swedish and Icelandic name, "mare" is
Norwegian and Danish.
In Newfoundland, as a visit from the "old hag" (Irish: Ag Rog).
In Mexico, as subida del muerto (the dead climbing on top).
In Greek, as mora the name has a Slavic root.
In German as Hexendrücken (witch pressing).
