Parasomnias: A Closer Look at Sleepwalking, Night Terrors, and REM Behavior Disorder

What Are Parasomnias?

Parasomnias are a category of sleep disorders characterized by abnormal or unusual behaviors, movements, emotions, perceptions, or dreams that occur during the transition into sleep, within sleep itself, or during arousal from sleep. Unlike insomnia or hypersomnia — which center on how much sleep a person gets — parasomnias are defined by what happens during sleep. For a broader orientation to the sleep disorder landscape, see how major sleep disorder categories differ.

Most parasomnias fall into one of two groups based on when they occur: NREM parasomnias, which arise during non-rapid eye movement sleep (typically the deeper early-night stages), and REM parasomnias, which emerge during REM sleep, when dreaming is most vivid. Understanding this distinction matters because it shapes both the presentation and the clinical approach.

Sleepwalking and Night Terrors: NREM Disorders of Arousal

Sleepwalking (somnambulism) occurs when a person partially arouses from deep NREM sleep and begins motor activity — walking, talking, or performing routine actions — while remaining largely unresponsive to the environment. Episodes typically happen in the first third of the night. The sleeper usually has no memory of the event afterward. Sleepwalking is most common in children, with prevalence estimates ranging from roughly 10 to 30 percent in childhood, though it can persist into or begin in adulthood.

Night terrors (sleep terrors) are episodes of sudden, intense fear accompanied by screaming, rapid heart rate, and signs of autonomic arousal. Like sleepwalking, they arise from deep NREM sleep, most often in children aged 3 to 8. A key distinguishing feature: the person is extremely difficult to console and typically has no recall of the episode by morning. This is meaningfully different from nightmares, which occur during REM sleep and are usually remembered.

Both conditions share a common mechanism — an incomplete transition out of deep sleep — and both are influenced by factors such as sleep deprivation, fever, stress, and certain medications. Injury risk during sleepwalking episodes is a genuine safety concern, particularly in unfamiliar environments. Curious about the underlying brain activity? Explore the neuroscience of sleep disorders for deeper context.

REM Sleep Behavior Disorder

REM sleep behavior disorder (RBD) is a REM parasomnia in which the normal muscle paralysis that accompanies REM sleep — called REM atonia — is absent or incomplete. As a result, individuals physically act out their dreams, sometimes vividly and forcefully. This may involve punching, kicking, shouting, or leaping out of bed, with the potential for injury to the sleeper or bed partner.

RBD is more common in men over 50, though it is not exclusive to that group. Notably, research has found a meaningful association between RBD and certain neurodegenerative conditions, including Parkinson's disease, Lewy body dementia, and multiple system atrophy. A diagnosis of RBD warrants discussion with a neurologist, as it can sometimes precede other neurological symptoms by years. This does not mean every person with RBD will develop a neurodegenerative condition, but it is clinically relevant information that a qualified provider should evaluate.

Accurate diagnosis of RBD typically involves an overnight sleep study (polysomnography) with video monitoring to confirm absent REM atonia. If you or a bed partner are concerned about forceful or injurious dream-enactment behaviors, a sleep specialist evaluation is the appropriate first step. For an overview of how sleep disorders are approached clinically, see treatment pathways for common sleep disorders.

Recognizing Patterns and Seeking Assessment

Many parasomnias go unrecognized for years because the person experiencing them is, by definition, largely unaware during episodes. Observations from a bed partner, parent, or caregiver are often the first signal that something warrants attention. Keeping a brief log of episode frequency, timing, duration, and any associated behaviors can be helpful when speaking with a clinician.

Parasomnias exist on a spectrum of severity. Isolated, infrequent episodes in otherwise healthy children are common and often resolve with age. Persistent or escalating episodes, those involving injury risk, or those beginning in adulthood deserve professional evaluation. Persistent sleep disruption generally deserves attention, regardless of the specific presentation.

This article is for general informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. If you have concerns about your sleep or the sleep of someone in your care, consult a qualified healthcare provider.