What is Sleep Paralysis
Sleep paralysis is a REM parasomnia characterized by temporary inability to move or speak during the transition between sleep and wakefulness, occurring either at sleep onset (hypnagogic) or upon awakening (hypnopompic), while the person remains fully conscious and aware of their surroundings. 1, 2, 3
Core Clinical Features
Sleep paralysis represents a dissociation between consciousness and muscle control, where REM sleep atonia (muscle paralysis) persists into the waking state. 3 The condition manifests with several characteristic symptoms:
- Motor paralysis: Complete inability to move voluntary muscles, though respiratory muscles remain functional 2, 3
- Preserved consciousness: Full awareness of surroundings despite inability to move or speak 4, 2
- Chest pressure sensation: Reported by 67.2% of affected individuals 2
- Difficulty vocalizing: Experienced by 81.0% during episodes 2
- Inability to open eyes: Occurs in 71.5% of cases 2
- Hallucinations: Frequently accompanying the paralysis, including visual, auditory, or tactile experiences 5, 1
Pathophysiology
The underlying mechanism involves dysfunction in the neural circuits controlling REM sleep, specifically the sublaterodorsal nucleus (subcoeruleus nucleus) in the brainstem, which normally induces muscle atonia during REM sleep. 3 Sleep paralysis occurs when this atonia fails to immediately resolve during the sleep-wake transition. 3
The condition reflects deficient monoaminergic regulation of REM sleep neural modulators, involving multiple brain regions including the forebrain, hypothalamus, and brainstem, along with various neurotransmitters. 6, 3
Classification and Prevalence
Sleep paralysis exists in two forms:
- Isolated sleep paralysis (ISP): Occurs without other sleep disorder symptoms, affecting approximately 8-20% of the general population 4, 2
- Narcolepsy-associated sleep paralysis: One component of the narcolepsy symptom tetrad (excessive daytime sleepiness, cataplexy, hypnagogic/hypnopompic hallucinations, and sleep paralysis) 5, 1
Most individuals experience their first episode between ages 16-20 years. 2
Critical Diagnostic Distinction
The American Academy of Sleep Medicine emphasizes that the presence of cataplexy plus hypnagogic paralysis indicates narcolepsy until proven otherwise and requires immediate sleep specialist referral. 1 This distinction is clinically urgent because narcolepsy requires different management and carries risks including motor vehicle accidents if untreated. 1
Distinguishing features include:
- Isolated SP occurs without excessive daytime sleepiness, cataplexy, or disrupted nocturnal sleep 1, 7
- Narcolepsy presents with the full symptom tetrad and requires polysomnography with multiple sleep latency testing showing mean sleep latency ≤8 minutes plus ≥2 sleep-onset REM periods 1
Common Misconceptions
A significant proportion (24.5%) of affected individuals are unaware the condition is called sleep paralysis, with 23.5% believing it is "just a dream." 2 The American Geriatrics Society warns against misdiagnosing sleep paralysis as psychosis, as SP occurs specifically at sleep-wake transitions with preserved insight, whereas psychotic hallucinations occur in fully awake states without insight. 1, 7
Precipitating Factors
Episodes are more likely to occur with: