Sleep paralysis demon is a term used to describe the hallucinations that some people experience during episodes of sleep paralysis. Sleep paralysis is a state in which one is conscious but in a complete state of full-body paralysis, during waking up or falling asleep. Sleep demons commonly involve temporary paralysis when falling asleep or waking up, and sensations may include chest pressure, hallucinations, and perceiving a presence in the room. Most descriptions of sleep paralysis demons have two things in common: being unable to move or speak, as well as the sense of being held down by a malevolent, often supernatural, intruder. Many people also describe a feeling of their chest being crushed. Sleep-related hallucinations have been described throughout recorded history, and different cultures have different explanations for sleep paralysis demons. Over 100 terms have been identified for these experiences, and they often reflect regional beliefs and traditions. Although the exact cause of sleep-related hallucinations remains unknown, many experts believe that hallucinations during sleep paralysis occur when people experience the vivid dreams of REM sleep while they are awake.