Parasomnias: Sleepwalking, Night Terrors, and Beyond

Last updated: June 2026 - Reviewed by the Apexzen editorial team

What are they? Parasomnias are a group of sleep disorders defined by undesirable physical events or experiences that occur during entry into sleep, within sleep, or during arousal from sleep. The American Academy of Sleep Medicine's International Classification of Sleep Disorders (ICSD-3) groups them by the stage of sleep they arise from.

During a parasomnia, the brain sits in a mixed state, partly asleep and partly aroused. That overlap is why a person can walk, talk, scream, or act out a dream while never truly waking, and why they often remember little or nothing afterward.

The three sub-families

NREM-related (disorders of arousal)

These arise out of deep non-REM sleep, usually in the first part of the night. They include sleepwalking (somnambulism), where a person carries out activities while asleep, and night terrors (pavor nocturnus), sudden episodes of intense fear with screaming and a racing heart. Confusional arousals, a milder cousin in which a person wakes disoriented and slow to respond, also belong here; a dedicated guide is in preparation.

REM-related

These arise from REM sleep, the stage where dreaming is most vivid. They include REM sleep behaviour disorder (RBD), in which the normal muscle paralysis of REM is lost and the sleeper physically acts out dreams, and recurrent isolated sleep paralysis, a brief inability to move or speak on falling asleep or waking. Nightmare disorder, marked by repeated distressing dreams that disrupt sleep, is also REM-related; a dedicated guide is in preparation.

Other parasomnias

A final group does not fit neatly into NREM or REM. It includes exploding head syndrome, the startling but harmless sensation of a loud noise or flash at sleep onset, and sleep enuresis (bedwetting during sleep). A dedicated guide to sleep enuresis is in preparation.

Safety first

Many parasomnias are harmless and need only reassurance, especially in children, who often outgrow them. The priority when episodes do occur is safety: keeping the bedroom clear of hazards, securing windows and stairs, and avoiding waking the person abruptly during an episode. Consistent sleep, limiting sleep deprivation, and managing stress and alcohol can reduce how often arousal-type episodes happen, since these are known triggers.

When to see a specialist

See a sleep specialist if episodes are frequent, dangerous, or distressing, if they cause injury to the sleeper or a bed partner, or if a parasomnia begins for the first time in adulthood, which can point to an underlying condition that needs evaluation. Acting out dreams in particular deserves prompt medical attention. A specialist can confirm the type, rule out other causes, and recommend an appropriate plan.

Part of: The Complete Atlas of Sleep Disorders. Explore the individual parasomnia guides linked above.

Sources: American Academy of Sleep Medicine. International Classification of Sleep Disorders, 3rd edition (ICSD-3). Darien, IL: AASM.

This article is for educational purposes only and is not medical advice. These statements have not been evaluated by the Food and Drug Administration. Apexzen products are not intended to diagnose, treat, cure, or prevent any disease. Consult a qualified healthcare provider for persistent or dangerous sleep problems.