During REM sleep, your brain temporarily paralyzes your muscles to prevent you from physically acting out your dreams.

During Rapid Eye Movement (REM) sleep, the brain becomes highly active—similar to waking consciousness—yet simultaneously triggers muscle paralysis through a process called REM atonia. This is controlled by the brainstem, specifically the subcoeruleus nucleus, which sends inhibitory signals to the spinal cord. These signals cause the release of neurotransmitters like glycine and GABA, which effectively silence the motor neurons controlling voluntary muscles.This paralysis is crucial for survival. Without it, people would physically act out their dreams, risking serious injury. Some individuals develop REM Sleep Behavior Disorder (RBD), a condition where they kick, punch, or run during sleep because this protective mechanism fails. Institutions like the Mayo Clinic study RBD as a potential early warning sign of neurological disease.Sleep paralysis happens when the brain's transition between REM sleep and wakefulness becomes misaligned. Research from Pennsylvania State University (2011) found that approximately 7.6% of the general population experiences at least one episode of sleep paralysis in their lifetime. During these episodes, the amygdala often becomes hyperactive, triggering intense fear or the sensation of a threatening presence.Though frightening, sleep paralysis is medically harmless. Episodes typically last from a few seconds to a few minutes before the brain restores muscle control. Understanding this biological quirk helps explain the sleep paralysis accounts that have inspired folklore and ghost stories across cultures for centuries.