Sleep Paralysis. What is it from a scientific perspective? Approximately 40% of people experience sleep paralysis at some point in their lives. They wake up without any ability to move. This happens if you awake during a REM sleep when your muscles are paralyzed. On rare occasions, people report seeing ghostly figures during sleep paralysis. One hypothesis links this phenomenon to an error in the way our brains construct a body model. Being unable to sense the paralyzed body, the brain mistakenly looks for it in the wrong place and therefore creates hallucinations.