This may be the scariest thing you ever read on SamadiMD. There is a condition called Sleep Paralysis. No this is not insomnia or sleep apnea, this is a condition or phenomenon that occurs either when falling asleep or being awakened. It's thought to be a mix-up of normal REM sleep (the deepest sleep we achieve throughout the night.) People who experience it are in some sense conscious and aware that they're aware they're in bed for example. But some part of their body believes they're still asleep, in particular their muscles. The muscles become paralyzed, something that happens in REM sleep. Some scientists believe this is an evolutionary mechanism that prevents people from acting out their dreams.