What Are Parasomnias? Sleepwalking, Sleep Terrors, and Nightmare Disorder Explained

Sleep
Written By Altruva Wellness Editorial Team

Published: 09/23/2026 | Last Updated: 09/23/2026

Parasomnias are unwanted movements, behaviors, or experiences that happen while you are falling asleep, asleep, or waking up. Sleepwalking, sleep terrors, and nightmare disorder are the three most people have heard of, and while they look very different from the outside, they share a single cause: the brain caught partway between sleep and wakefulness. This article explains what parasomnias are, why the three headline conditions behave so differently, what triggers them, what to do during an episode, and when they warrant a visit to a sleep specialist.

What Parasomnias Are

A parasomnia is a sleep disorder involving abnormal behaviors, movements, emotions, or perceptions that occur during sleep or during the transitions into and out of it. The sleeper is not fully awake and usually not fully asleep either. Examples include sleepwalking, sleep terrors, sleep talking, sleep paralysis, and nightmare disorder.

The simplest way to understand them is as a state mix-up. Normally the brain moves cleanly between wakefulness, light sleep, deep sleep, and dream sleep. In a parasomnia, part of the brain is awake enough to walk, talk, or feel terror, while other parts remain asleep. That is why a sleepwalker can navigate a hallway with open eyes and remember none of it, and why a nightmare can feel entirely real until the moment you wake.

According to Cleveland Clinic, parasomnias are more common in children than adults but can occur at any age, and the deep-sleep types tend to run in families. Most are harmless and fade with time. A minority are disruptive, dangerous, or a sign of something else going on, which is why knowing the categories matters.

One factor sits underneath nearly all of them: not enough sleep. Deprivation deepens the deep-sleep stages and fragments the rest, both of which make state mix-ups more likely. Our explainer on how sleep debt builds and whether you can repay it is the natural companion to this piece, because the single most effective step for most parasomnias is simply sleeping more.

The NREM vs. REM Split That Explains Everything

Parasomnias are grouped by the sleep stage they come from, and that grouping predicts almost everything about how they behave.

Deep-Sleep Parasomnias (NREM)

Sleepwalking, sleep terrors, and confusional arousals arise from the deepest stage of non-REM sleep. The CMAJ review on parasomnias describes them as partial arousals: the body wakes enough to act while the brain's conscious, memory-forming regions stay offline. Because deep sleep is concentrated early in the night, these episodes typically happen in the first third of sleep, often within one to two hours of falling asleep.

The sleeper's eyes are usually open with a glassy, unfocused look. They do not respond normally, are hard to wake, and remember little or nothing the next morning. These parasomnias are most common between roughly ages 5 and 25 and usually resolve with age.

Dream-Sleep Parasomnias (REM)

Nightmare disorder, recurrent sleep paralysis, and REM sleep behavior disorder arise from dream sleep. REM is concentrated in the second half of the night, so these episodes cluster in the last third of sleep. The eyes are closed, the person usually wakes fully and quickly, and they remember the dream content vividly.

This group behaves differently in one more important way. The StatPearls clinical reference notes that REM parasomnias in adults, particularly REM sleep behavior disorder, can be associated with neurological conditions and warrant evaluation rather than reassurance. Sleep paralysis is the most common REM parasomnia and the most misunderstood; our breakdown of why sleep paralysis feels so threatening and what stops it covers it in full.

The two groups side by side:

  • Timing: NREM in the first third of the night; REM in the last third

  • Eyes: NREM open and glassy; REM closed

  • Memory: NREM little or none; REM vivid recall

  • Waking: NREM confused and hard to rouse; REM alert almost immediately

  • Typical age: NREM childhood and young adulthood; REM more often later in life

Sleepwalking

Sleepwalking, or somnambulism, is getting up and moving around while asleep. Mayo Clinic notes it usually occurs one to two hours after falling asleep, rarely during naps, and a typical bout lasts several minutes, though it can run longer.

Most episodes are mundane: sitting up, wandering the room, mumbling. A sleepwalker may also perform routine tasks like getting dressed or eating, and in rarer cases leave the house, drive a car, or engage in behavior they would never choose awake. They will not remember any of it. Some people who sleepwalk also have sleep terrors, and a sleepwalking episode can begin as one.

Sleepwalking is far more common in children and usually outgrown by the teen years. When it starts or persists in adulthood, Mayo Clinic notes it is more likely to be confused with, or occur alongside, another sleep disorder or medical condition, which changes how it should be evaluated.

The main concern is injury. Falls down stairs, walking into furniture, going outside, and using the kitchen are all documented risks. For households with a sleepwalker, the practical response is environmental: locked doors and windows, cleared floors, gates on stairs, and no sleeping on upper bunks.

Sleep Terrors

Sleep terrors, also called night terrors, are episodes of screaming, crying, or intense fear during sleep. Mayo Clinic describes the classic picture: the person often sits bolt upright, looking terrified, sometimes thrashing or waving arms and legs. Cleveland Clinic adds the physical signs, a racing heart, dilated pupils, rapid breathing, and sweating, and notes episodes usually last around 30 seconds but can run a few minutes.

The defining feature is that the person is not awake. They do not respond to comfort, are hard to rouse, and if woken are confused. In the morning they remember nothing, which is why sleep terrors are typically far more distressing for the parent or partner watching than for the person having them.

How they differ from nightmares:

  • Stage: deep NREM sleep, early in the night

  • Awareness: not awake, cannot be consoled

  • Memory: none the next day

  • Recall: no dream story attached, just fear

  • Age: mostly young children; less common in adults

Sleep terrors share triggers with sleepwalking, and in adults the two most common are sleep deprivation and alcohol, both of which alter the depth and structure of the first half of the night. Cutting late drinks and keeping a steady schedule is the first-line fix, and the timing structure in our walkthrough of the countdown routine that removes the biggest sleep disrupters handles both at once.

Nightmare Disorder

Nightmares are disturbing dreams that wake you and leave you anxious or frightened. Nearly everyone has them occasionally. Mayo Clinic notes they typically begin in children between ages 3 and 6 and become less common after 10, though some people have them throughout life.

Nightmare disorder is different in degree, not kind. Mayo Clinic defines it as nightmares that happen often, cause real distress, routinely disrupt sleep, impair daytime functioning, or create fear of going to sleep. Occasional bad dreams do not qualify. A pattern that changes how you sleep and live does.

Because nightmares occur in REM, they cluster in the second half of the night, and the person wakes fully and remembers the dream in detail. That vivid recall is the clearest way to tell a nightmare from a sleep terror. Triggers include stress and anxiety, major life changes, trauma, and post-traumatic stress disorder, where nightmares are a core symptom. The CMAJ review also flags certain medications, including some antidepressants and blood pressure drugs, as causes worth reviewing with a prescriber.

The most immediate practical problem with nightmares is what happens after: lying awake at 3 a.m. with a racing heart and a mind that will not settle. Our step-by-step guide to getting back to sleep after a middle-of-the-night wake-up is built for exactly that moment, and it works after a nightmare as well as after any other awakening.

What Triggers Parasomnias

For the deep-sleep types, the underlying tendency is largely inherited. What determines whether it shows up on a given night is the set of triggers stacked on top of it. The most common, drawn from Cleveland Clinic and the CMAJ review:

  • Sleep deprivation: the single biggest trigger, because it deepens and destabilizes NREM sleep

  • Stress and anxiety: raises arousal during sleep and fuels nightmares specifically

  • Fever and illness: especially in children

  • Alcohol: fragments sleep and increases arousals in the first half of the night

  • Certain medications: sedatives, some antidepressants, and others; worth a conversation with a prescriber

  • Irregular schedules: shift work, jet lag, and inconsistent bedtimes

  • Untreated breathing problems during sleep: repeated micro-arousals can set off episodes

  • Family history: strongly predictive for sleepwalking and sleep terrors

The breathing trigger deserves attention because it is common, treatable, and often missed. Obstructive sleep apnea repeatedly pulls the brain partway toward wakefulness, which is precisely the state that produces NREM parasomnias, and the CMAJ review notes the association directly. If parasomnias occur alongside loud snoring, gasping, or heavy daytime sleepiness, our explainer on how sleep apnea quietly disrupts the whole body covers the signs to look for.

For the deep-sleep parasomnias, this list is the treatment plan. There is no medication that reliably cures sleepwalking or sleep terrors in otherwise healthy people. Removing triggers is what reduces episodes.

What to Do During an Episode

For sleepwalking or a sleep terror, the instinct is to wake the person. The better approach is to guide them gently back to bed and let the episode end on its own, because someone woken mid-episode is confused, disoriented, and occasionally combative. Practical steps:

  • Speak calmly and simply; do not shout or shake

  • Steer, do not grab: light guidance by the shoulders back toward bed

  • Do not try to reason with them or ask questions; they cannot process it

  • Keep the environment safe in advance: locks, gates, cleared floors

  • Note the time; episodes that consistently happen at the same point in the night can sometimes be preempted with a brief planned wake-up 15 to 30 minutes before

For a nightmare, the person is awake and can be reached. Brief reassurance, a light touch, a sip of water, and low light are enough. Detailed discussion of the dream at 3 a.m. tends to keep the mind active; save it for morning if it needs discussing at all.

When to See a Sleep Specialist

Most parasomnias in children resolve on their own and need nothing more than a mention at a routine checkup. Adults and caregivers should seek evaluation when any of these apply:

  • Episodes are frequent, or increasing in frequency

  • Anyone has been injured, or the behavior carries clear injury risk (leaving the house, using the kitchen, driving)

  • Daytime functioning is affected by disrupted sleep

  • Parasomnias begin or return in adulthood, especially with no obvious trigger

  • The person appears to act out dreams with punching, kicking, or shouting, which points to REM sleep behavior disorder and, per the StatPearls reference, can be associated with neurological conditions that benefit from early evaluation

  • Nightmares are linked to trauma or PTSD symptoms

A sleep specialist may recommend an overnight sleep study, called polysomnography, which records brain activity, eye movement, muscle tone, and breathing. It is the only way to see which stage an episode comes from and to rule out apnea or seizures that can mimic parasomnias. For nightmare disorder, the first-line treatments are behavioral: stress reduction, a consistent wind-down, and, for persistent cases, a structured technique called imagery rehearsal therapy delivered by a clinician. The tools in our guide to settling a racing mind before bed cover the self-directed end of that spectrum.

FAQ

Are parasomnias dangerous?

Most are not, especially in children. The risks come from injury during sleepwalking, from the exhaustion of chronically disrupted sleep, and, in adults, from REM sleep behavior disorder, which can involve violent movements and may signal an underlying neurological condition.

Should you wake someone who is sleepwalking?

Generally no. Guide them gently back to bed instead. Waking a sleepwalker is not physically harmful, but they will be confused and disoriented, and the episode usually ends on its own within minutes.

What is the difference between a night terror and a nightmare?

A night terror happens in deep sleep early in the night; the person is not awake, cannot be comforted, and remembers nothing. A nightmare happens in REM sleep later in the night; the person wakes fully and remembers the dream clearly.

Do children grow out of parasomnias?

Usually. Sleepwalking and sleep terrors typically fade by the teen years, and nightmares become less common after age 10. Persistence into adulthood or a new onset in adulthood is worth evaluating.

Can adults suddenly develop parasomnias?

Yes. Adult-onset parasomnias are more likely to be linked to another factor, such as sleep deprivation, alcohol, a new medication, untreated sleep apnea, or, for REM-related types, a neurological condition. New adult episodes should be discussed with a healthcare provider.

Final Thoughts

Parasomnias are unsettling to witness and, for nightmares, unsettling to experience, but the majority are the brain's wiring showing through under stress rather than a sign of anything broken. Once you know which category an episode belongs to, most of the mystery disappears: early in the night, eyes open, no memory means deep sleep; late in the night, vivid recall means REM.

The practical response for the common types is unglamorous. Sleep enough, keep the schedule steady, limit alcohol, manage stress, and make the bedroom safe. Those steps address the triggers that turn a latent tendency into a recurring problem, and for many people they are the entire treatment.

Wearables cannot diagnose parasomnias; they estimate sleep stages from movement and heart rate rather than reading brain activity, so an episode will show up as a vague awakening at best. What they can do is confirm whether the sleep-deprivation trigger is in play, and our ranked guide to sleep trackers that reliably capture timing and awakenings is useful for that specific job, with a sleep study reserved for the actual diagnosis.

If episodes are frequent, escalating, dangerous, or new in adulthood, the right move is a sleep specialist, not more searching. The conditions are well understood, and the evaluation is routine.

By Altruva Wellness Editorial Team

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Disclaimer: This content is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making changes to your wellness routine.

Altruva Wellness Editorial Team http://www.altruvawellness.com
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