Sleep Paralysis: REM Atonia Persisting Into Wakefulness
Sleep paralysis affects 7.6% of the general population; it represents persistence of REM muscle atonia into wakefulness; hallucinations occur in ~75% of episodes; linked to sleep deprivation and disrupted schedules.
| Measure | Value | Unit | Notes |
|---|---|---|---|
| Lifetime prevalence (general population) | 7.6 | % of people | Sharpless & Barber 2011 meta-analysis; higher in students and psychiatric patients |
| Recurrent sleep paralysis prevalence | ~1 | % of population | Isolated sleep paralysis is more common; recurrent is a separate clinical entity |
| Episode duration | Seconds to 10 | minutes | Most episodes last <5 minutes; rarely up to 20+ min |
| Hallucination presence during SP | ~75 | % of episodes | Visual (shadow/figure), tactile (chest pressure), and auditory hallucinations |
| Risk factors | Sleep deprivation, irregular schedule, supine position | precipitants | Supine sleeping significantly increases risk vs lateral position |
Mechanism
Sleep paralysis represents a dissociated state where elements of REM sleep (atonia) and wakefulness coexist simultaneously. During normal REM sleep, two processes co-occur:
- The cortex is activated (desynchronized EEG) and produces dreaming
- The brainstem’s glycinergic/GABAergic neurons suppress motor neurons (atonia) to prevent movement
In sleep paralysis, the cortex returns to wakefulness (conscious awareness resumes) before the brainstem atonia circuit deactivates. The individual is aware and perceiving their environment, but the motor inhibition remains in force.
Types and Timing
Hypnagogic sleep paralysis: occurs at sleep onset, transitioning from wake into sleep (less common) Hypnopompic sleep paralysis: occurs at awakening, transitioning from sleep to wake (more common)
Both involve the same mechanism of REM-wake state dissociation, but at different transition points.
Hallucinations
Approximately 75% of sleep paralysis episodes are accompanied by hallucinations — often highly realistic and terrifying. Cheyne et al. (1999) classified three types:
- Intruder hallucinations: sensing a presence in the room, threatening figure, shadowy intruder; driven by hyperactive threat-detection systems
- Incubus hallucinations: pressure on the chest, difficulty breathing, sense of being crushed; historically called “old hag” phenomena (Old English: maere)
- Vestibular-motor hallucinations: sensations of flying, floating, falling, or leaving the body; REM sleep’s vestibular activity perceived without visual context
These hallucinations explain the cross-cultural mythology of nocturnal visitors: Old Hag (English), Kanashibari (Japanese), Ale (Danish), Ogun Oru (Nigerian Yoruba) — all describe nocturnal paralysis with a malevolent presence.
Risk Factors and Prevalence
| Population | Prevalence |
|---|---|
| General population (lifetime) | 7.6% |
| University students | 28–38% |
| Psychiatric patients | 31.9% |
| Narcolepsy patients | 17–66% |
Precipitating factors include: sleep deprivation, irregular sleep-wake schedule, jet lag, supine sleeping position, increased stress, and substance use.
Related Pages
Sources
- Sharpless BA & Barber JP — Lifetime prevalence rates of sleep paralysis. Sleep Med Rev (2011)
- Cheyne JA et al. — Hypnagogic and hypnopompic hallucinations during sleep paralysis. Neuropsychologia (1999)
- Jalal B et al. — Cultural frequency and phenomenology of sleep paralysis in Denmark, Japan, China, and Denmark. Psychol Med (2015)
- Dahlitz M & Parkes JD — Sleep paralysis. Lancet (1993)
Frequently Asked Questions
Why does sleep paralysis happen?
Sleep paralysis occurs when the brain awakens from REM sleep but the muscle atonia (paralysis) that normally accompanies REM persists. During REM, brainstem glycinergic and GABAergic neurons hyperpolarize motor neurons to prevent acting out dreams. Occasionally, consciousness returns before the atonia dissipates, leaving the person aware but unable to move, speak, or react — typically lasting seconds to minutes.
Is sleep paralysis dangerous?
Sleep paralysis is not physically dangerous. It cannot cause death or lasting paralysis. The muscle atonia is temporary and dissipates within seconds to minutes. Breathing continues normally via the diaphragm (which is exempt from REM atonia). The psychological distress can be significant due to hallucinations and panic, but the underlying physiology is benign.
How do you stop sleep paralysis?
During an episode: attempting small movements (wiggling fingers or toes) can help terminate the atonia. Some people report that vigorous eye movements help. Prevention focuses on risk factor reduction: maintain consistent sleep schedule, ensure adequate sleep quantity, avoid supine (back) sleeping, reduce sleep deprivation. Recurrent sleep paralysis associated with narcolepsy requires specialist evaluation.