Strange Sleeping Experiences
How it feels: The person wakes up at night and cannot move. Added to this are frightening hallucinations and a feeling that there is someone else in the room. In antiquity, this state was associated with mischiefs of evil spirits.
Why it happens: Normally, when we fall asleep, we are paralyzed so that we don’t sleepwalk and such. With sleep paralysis, our muscles "turn off" when the brain is awake.
Approximately 7% of the population have experienced sleep paralysis at least once . They say this is more likely when sleeping on the back.