What Is Sleep Paralysis?

“Sleep paralysis” (colloquially known as “ghost pressing on the bed”) refers to a phenomenon wherein a person suddenly becomes conscious while falling asleep or waking up but is temporarily unable to move their body. In sleep neurology, this is classified as a symptom of sleep paralysis.

Sleep paralysis occurs during the rapid eye movement (REM) stage of the sleep cycle—the phase in which deep sleep begins and vivid dreaming takes place. During REM sleep, dream activity intensifies while voluntary skeletal muscles become temporarily paralyzed. This transient paralysis may occasionally persist briefly after awakening, leaving individuals unable to move immediately upon regaining consciousness.

During REM sleep, skeletal muscles—except for those controlling respiration and eye movements—are maintained in a state of extremely low muscle tone. This physiological inhibition serves a protective function, preventing individuals from physically acting out their dreams and potentially harming themselves or others nearby.

In sleep paralysis, however, consciousness re-emerges prematurely during REM sleep while skeletal muscles remain in this low-tone state, resulting in a temporary disconnect between conscious intent and motor control. The unusual physical sensations—such as immobility, pressure on the chest, or difficulty breathing—may be misinterpreted by the brain, especially when compounded by fear or anxiety, leading to vivid hallucinations.

Sleep paralysis can occur during both daytime naps and nighttime sleep. Importantly, it bears no relation whatsoever to supernatural phenomena. Medically, it is formally termed “sleep paralysis.”