Sleep paralysis is a phenomenon in which people, either when falling asleep or wakening, temporarily experience inability to move, similar to when an arm or leg goes to sleep, but not associated with numbness. More formally, it is a transition state between wakefulness and rest characterized by complete muscle atonia (muscle weakness). It can occur at sleep onset or when awakening. It is believed a result of disrupted REM sleep, which is normally characterized by complete muscle atonia that prevents individuals from acting out their dreams. -Wikipedia
Anybody ever wake up then find you can not move? Felt it hard to breathe, like something was pressing down on your chest? You can see and hear what is going on. Just laying there frozen without being able to go back to sleep or fully wake up.