Why do we see monsters during sleep paralysis?

Have you ever woken up at 3 AM unable to move, with a heavy shadow on your chest? This is sleep paralysis. It’s not a demon—it’s a terrifying glitch in human sleep linked to REM atonia and the Threat Simulation Theory. We explore the evolutionary biology behind nightmares, why your brain chemically paralyzes your body, and how this ancient survival mechanism kept your ancestors alive.