Sleep researchers conclude that, in most cases, sleep paralysis is simply a sign that your body is not moving smoothly through the stages of sleep. Rarely is sleep paralysis linked to deep underlying psychiatric problems.
Over the centuries, symptoms of sleep paralysis have been described in many ways and often attributed to an "evil" presence: unseen night demons in ancient times, the old hag in Shakespeare's "Romeo and Juliet," and alien abductors. Almost every culture throughout history has had stories of shadowy evil creatures that terrify helpless humans at night. People have long sought explanations for this mysterious sleep-time paralysis and the accompanying feelings of terror.