From New York Post:
It’s the stuff of nightmares.
You wake up, and you can’t move your body. A shadowy figure looms over you, but it feels too real to be a dream. If you’ve experienced this, you might have had a sleep paralysis hallucination. The hallucinations typically happen when someone passes between the state of being asleep in the rapid-eye movement stage and being awake, according to the Sleep Foundation. The body is temporarily paralyzed during these hallucinations because the body doesn’t move when a person is in REM. The brief lack of muscle control is called atonia. [temporary internet glitch: please note that some have issue when click back; ignore flash screens that say “continue reading”]