What Are Parasomnias?
Parasomnias are a category of sleep disorders defined by abnormal experiences or behaviors during sleep, during sleep-wake transitions, or during partial arousals from sleep. They differ from other sleep disorders in that the primary complaint is not about sleep quality or duration, but about what happens during sleep itself.
The most fundamental organizing principle for parasomnias is the sleep stage in which they arise:
| Category | Sleep Stage | Examples | Memory of Event |
|---|---|---|---|
| NREM parasomnias (disorders of arousal) | N3 slow-wave sleep (first third of night) | Sleepwalking, night terrors, confusional arousals | None or minimal |
| REM parasomnias | REM sleep (mostly second half of night) | Nightmares, REM behavior disorder | Vivid (nightmares); absent (RBD) |
| Other parasomnias | Any stage / transitions | Sleep paralysis, hypnic jerks, sleep talking | Variable |
NREM Parasomnias (Disorders of Arousal)
NREM parasomnias arise from incomplete arousals from deep (N3) slow-wave sleep. During these episodes, the brain is in a peculiar hybrid state — aroused from deep sleep but not fully conscious. Motor systems are active, but the cortex (responsible for conscious awareness, judgment, and memory encoding) remains partially asleep. This explains the key features shared by all NREM parasomnias:
- Occur in the first third of the night (when slow-wave sleep predominates)
- Person appears awake but is not fully conscious — eyes may be open, talking may occur
- Person is difficult to fully awaken
- No memory of the episode the next morning
- Triggered by factors that deepen slow-wave sleep or fragment it: sleep deprivation, fever, medications, stress, alcohol
- More common in children (who have more slow-wave sleep) and often remit with age
Sleepwalking (Somnambulism)
Sleepwalking involves ambulation and other complex behaviors during partial arousal from N3 sleep. Episodes can range from simply sitting up in bed to wandering around the home, leaving the house, driving (rare but documented), or engaging in complex activities. The eyes are usually open and appear glassy. The person may mumble or respond minimally to questions.
Prevalence: Approximately 3–4% of adults (higher in children: ~17% at some point). Strongly familial.
Triggers: Sleep deprivation (the most important modifiable trigger — increases the depth and amount of slow-wave sleep), fever, stress, alcohol, sedative medications, bladder pressure, sleep apnea (arousals from apnea can trigger NREM events).
Safety: Despite popular belief, it is not dangerous to wake a sleepwalker — it may cause brief confusion and distress, but is not harmful. What IS dangerous is the sleepwalking itself: falling down stairs, walking into traffic, operating appliances, and in rare cases violence (sleep-related violence is a legal area with significant complexity). Environment safety measures are important for frequent sleepwalkers: door alarms, stair gates, securing windows, removing hazardous objects from the sleep path.
Management: Improving sleep quality (treating coexisting sleep disorders, ensuring adequate sleep duration), scheduled awakening therapy (briefly waking the person 15–20 minutes before the typical episode time for 3–5 weeks), stress reduction, and avoiding triggers. For severe or potentially dangerous cases, medications (low-dose clonazepam, melatonin) may be prescribed.
Sleep Terrors (Night Terrors)
Sleep terrors are episodes of sudden, intense fear arising from N3 sleep. The person sits up abruptly, screams or cries, appears terrified, shows autonomic activation (rapid heart rate, sweating, flushing, dilated pupils), and is inconsolable for several minutes — typically 1–10 minutes. After the episode, the person returns to sleep with no memory of the event.
Night terrors are often confused with nightmares, but they are fundamentally different:
| Feature | Night Terrors | Nightmares |
|---|---|---|
| Sleep stage | NREM (N3 deep sleep) | REM sleep |
| Timing | First third of night | Last third of night |
| Appearance during episode | Eyes open, screaming, terrified — but not "there" | Typically quiet; person may not stir |
| Memory | None — no recall of episode | Vivid — person wakes and recalls the nightmare |
| Consol-ability | Very difficult during episode | Usually calms quickly on waking |
| Common in | Children (peak 4–12); can occur in adults | All ages; peaks in adults under stress |
Management: In children, night terrors typically resolve with age. Triggers include sleep deprivation, fever, and stress — addressing these is the primary approach. For frequent episodes, scheduled awakening therapy is effective. In adults, evaluation for stress, anxiety, PTSD, and coexisting sleep disorders is important. Medications (low-dose benzodiazepines or SSRIs) may be used for severe cases.
Confusional Arousals
The most common NREM parasomnia. The person appears to wake from deep sleep but is confused, disoriented, speaks incoherently, may appear distressed, and behaves in a disorganized way — sitting up, looking around blankly, sometimes responding minimally to their name — before returning to sleep. Episodes last minutes. Like sleepwalking and night terrors, there is no memory of the event. Very common in children; can persist into adulthood, particularly when sleep deprived.
REM Parasomnias
Nightmare Disorder
Nightmares are vivid, disturbing dreams that typically occur during REM sleep. They often involve threats, danger, embarrassment, or loss, and are sufficiently distressing to wake the dreamer, who typically has clear recall of the dream content. Occasional nightmares are universal. Nightmare disorder is diagnosed when nightmares are frequent (multiple times per week), recurrent, cause significant distress, and impair daytime functioning or cause reluctance to go to sleep.
Causes and triggers:
- PTSD (nightmares are a DSM criterion for PTSD — often replaying traumatic events)
- Anxiety and stress
- Medications: antidepressants (particularly those affecting REM), beta-blockers, some blood pressure medications, nicotine patches
- Alcohol withdrawal (causes REM rebound)
- Sleep deprivation followed by recovery sleep (REM rebound)
- Fever
Treatments:
- Image Rehearsal Therapy (IRT): The most evidence-based treatment for chronic nightmare disorder. The patient writes out the nightmare narrative, then deliberately creates a new, different ending for the dream and rehearses the new version during waking hours. Reduces nightmare frequency and intensity significantly in clinical trials.
- Prazosin: An alpha-1 adrenergic blocker originally used for blood pressure, shown in multiple RCTs to reduce nightmare frequency and severity in PTSD. First-line pharmacological treatment for PTSD-related nightmares.
- PTSD treatment: When nightmares are PTSD-related, trauma-focused psychotherapy (EMDR, CPT, PE) that addresses the underlying trauma is the definitive treatment.
REM Sleep Behavior Disorder (RBD)
RBD is one of the most clinically important parasomnias because of its neurological significance. In normal REM sleep, the brain generates a state of motor atonia — nearly complete muscle paralysis — that prevents the body from acting out dream content. In RBD, this atonia mechanism fails. The sleeper literally acts out their dreams — shouting, punching, kicking, leaping out of bed, and performing complex movements — while in REM sleep. The person is typically dreaming of being attacked or chased.
Why RBD requires urgent attention: A groundbreaking finding in sleep medicine is that idiopathic RBD (without a known cause) is a significant prodromal marker for neurodegenerative disease. Approximately 80–90% of people with idiopathic RBD eventually develop a synucleinopathy — Parkinson's disease, dementia with Lewy bodies, or multiple system atrophy — with a median lead time of 10–15 years. This means RBD is a window for potential neuroprotective intervention as those therapies are developed. Any adult with suspected RBD should receive neurological evaluation.
Symptoms of RBD: Complex, often violent behaviors during sleep in the second half of the night (when REM predominates); partner reports punching, kicking, yelling; vivid action-filled dreams; injuries to self or partner; the person can recall the dream content if woken during or shortly after an episode.
Diagnosis: Polysomnography with synchronized video recording is required — it demonstrates loss of normal REM atonia with complex motor behaviors.
Management:
- Safety first: Pad the bed frame, remove sharp objects, place mattress on floor if falls are occurring, partner may need to sleep separately temporarily
- Clonazepam: Low-dose (0.25–2 mg) benzodiazepine at bedtime reduces RBD behaviors in 90% of patients. Long-term treatment required.
- Melatonin (high dose, 3–12 mg): An alternative or adjunct to clonazepam with fewer side effects, particularly useful in older adults where benzodiazepine risks are higher
- Review medications: Some antidepressants (SSRIs, SNRIs, TCAs) can trigger or worsen RBD; if suspected, discuss with prescriber
Sleep Talking (Somniloquy)
Sleep talking occurs in any sleep stage and is common — affecting approximately 66% of people at some point in their lives. It ranges from simple mumblings to elaborate, apparently coherent speech. It can occur in NREM or REM sleep; REM sleep talking is often related to dream content. Sleep talking is generally benign, though it can be disruptive to bed partners. It can be increased by fever, stress, sleep deprivation, and some medications. No specific treatment is required unless it's causing significant partner disruption or associated with other parasomnias that require evaluation.
Scheduled Awakening Therapy
For frequent NREM parasomnias (sleepwalking, sleep terrors), scheduled awakening therapy is an effective behavioral intervention:
- Track the timing of episodes over 1–2 weeks (using a sleep log or video monitoring)
- Set an alarm for 15–20 minutes before the typical episode time
- Gently (but fully) wake the person, ensure they're conscious for a few minutes, then allow them to return to sleep
- Continue for 3–5 weeks, then gradually discontinue
This works by disrupting the deep N3 sleep period from which NREM parasomnias arise, preventing the partial arousal that triggers the episode.