I'm curious if someone would like to explain more about sleep paralysis..why it occurs?

REM-related: Paralysis of most of the muscles is normal during rem sleep. This prevents us from acting out our dreams. Sleep paralysis refers to episodes in which this paralysis persists for a short time after someone wakes up. It can also occur just as one is falling asleep. Rare episode are normal. It may occur more often in someone who is sleep-deprived, and some narcoleptics have frequent episodes.