Happens when waking up before REM sleep is finished only to find yourself paralysed. Someone experiencing this cannot move, talk, scream out for help and some cannot breathe.

Medically, little is know of the cause of sleep paralysis. Experienced worldwide and throught history, SP occurs to otherwise normal people at the onset, or the end of REM (rapid eye movement) sleep. Simply stated, SP seems to be an experience opposite sleep walking. Rather than your body unconscincely moving mimicing a dream, your conscince mind will be rendered unable to move your body. A subject will suddenly become completely aware of his/her surroundings, but will be unable to move their body or even wake up. Hallucinations and intense fear accompany the experience, as subjects may scence an evil presence that often sits on the subject's chest and interferes with the ability to breathe normally. The physical form of the presence varies from time period and culture, older instances involved witches, or "hags" and many new cases involve aliens. These subjects will experience many of the stereotypical events of an alien abduction, such as paralysis, floating sensation, and auditory hallucinations. The event can last from several seconds, to several minutes, with the subject either falling deeper into sleep, or snaping out and waking. The experience usually leaves the subject confused and disoriented and often, even after waking, the subject believes the event to have been an actual experience. SP is not known to be harmfull, and paralysis has never been know to adversly effect invoulentary muscles such as heart or lungs, although an elevated heart rate may occur from the scence of fear. If you have experienced sleep paralysis, it is important to keep in mind that it is largely a dream. Any experiences that take place are created by your mind. Having a bit of knowledge of what is actually going on, often helps subjects to deal with it.