Merck Manual

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Richard J. Schwab

, MD, University of Pennsylvania, Division of Sleep Medicine

Reviewed/Revised May 2022
Topic Resources

Parasomnias are undesirable behaviors that occur during entry into sleep, during sleep, or during arousal from sleep. Diagnosis is clinical. Treatment may include drugs and psychotherapy.

For many of these disorders, history and physical examination can confirm the diagnosis.


Sitting, walking, or other complex behaviors occur during sleep, usually with the eyes open but without evidence of recognition. Somnambulism is most common during late childhood and adolescence and occurs after and during arousal from nonrapid eye movement (NREM) stage N3 sleep. Prior sleep deprivation and poor sleep hygiene increase the likelihood of these episodes, and risk is higher for 1st-degree relatives of patients with the disorder. Episodes may be triggered by factors that cause arousals during sleep (eg, caffeine, other stimulant drugs and substances, behaviors that disrupt sleep) or that enhance N3 sleep (eg, prior sleep deprivation, excessive exercise).

Patients may mumble repetitiously, and some injure themselves on obstacles or stairs. Patients do not remember dreaming after awakening or the following morning and usually do not remember the episode.

Treatment of somnambulism is directed at eliminating the triggers for these episodes. It also involves protecting patients from injury—eg, by using electronic alarms to awaken patients when they leave the bed, using a low bed, installing door alarms, and removing sharp objects from the bedside and obstacles from the bedroom. Occasionally, patients are advised to sleep on mattresses on the floor.

Benzodiazepines, particularly clonazepam 0.5 to 2 mg orally, at bedtime can help if behavioral measures are not completely effective, but these drugs have significant adverse effects.

Sleep (night) terrors

During the night, patients suddenly scream, flail, and appear to be frightened and intensely activated. Episodes can lead to sleepwalking. Patients are difficult to awaken. Sleep terrors are more common among children and occur when children are partially aroused or are awakened from N3 sleep; thus, they do not represent nightmares. In adults, sleep terrors can be associated with psychologic problems or alcohol use disorder.

For children, parental reassurance is often the mainstay of treatment. If daily activities are affected (eg, if school work deteriorates), intermediate- or long-acting oral benzodiazepines (eg, clonazepam 1 to 2 mg, diazepam 2 to 5 mg) at bedtime may help, but these drugs have significant adverse effects. Adults may benefit from psychotherapy or drug treatment.


Children are more likely to have nightmares than adults. Nightmares occur during REM sleep, more commonly when fever, excessive fatigue, or mental distress is present or after alcohol has been ingested.

Treatment of nightmares is directed at any underlying mental distress.

Rapid eye movement (REM) sleep behavior disorder

Verbalization (sometimes profane) and often aggressive movements (eg, waving the arms, punching, kicking) occur during REM sleep. These behaviors may represent acting out dreams by patients who, for unknown reasons, do not have the atonia normally present during REM sleep. Patients are aware of having vivid dreams when they awaken after the behaviors.

REM sleep behavior disorder is more common among older people, particularly those with degenerative disorders of the central nervous system (CNS)—eg, Parkinson disease Parkinson Disease Parkinson disease is a slowly progressive, degenerative disorder characterized by resting tremor, stiffness (rigidity), slow and decreased movement (bradykinesia), and eventually gait and/or... read more , Alzheimer disease Alzheimer Disease Alzheimer disease causes progressive cognitive deterioration and is characterized by beta-amyloid deposits and neurofibrillary tangles in the cerebral cortex and subcortical gray matter. Diagnosis... read more , vascular dementia Vascular Cognitive Impairment and Dementia Vascular cognitive impairment and dementia is acute or chronic cognitive deterioration due to diffuse or focal cerebral infarction that is most often related to cerebrovascular disease. (See... read more , multiple system atrophy Multiple System Atrophy (MSA) Multiple system atrophy is a relentlessly progressive neurodegenerative disorder causing pyramidal, cerebellar, and autonomic dysfunction. It includes 3 disorders previously thought to be distinct... read more , progressive supranuclear palsy Progressive Supranuclear Palsy (PSP) Progressive supranuclear palsy is a rare, degenerative central nervous system disorder that progressively impairs voluntary eye movements and causes bradykinesia, muscular rigidity with progressive... read more Progressive Supranuclear Palsy (PSP) . Similar behavior can occur in patients who have narcolepsy Narcolepsy Narcolepsy is characterized by chronic excessive daytime sleepiness, often with sudden loss of muscle tone (cataplexy). Other symptoms include sleep paralysis and hypnagogic and hypnopompic... read more or who take norepinephrine reuptake inhibitors (eg, atomoxetine, reboxetine, venlafaxine). In patients with REM sleep behavior disorder, synuclein accumulates in neurons, as occurs in neurodegenerative disorders such as Parkinson disease, multiple system atrophy, and dementia with Lewy bodies Dementia with Lewy Bodies and Parkinson Disease Dementia Lewy body dementia includes clinically diagnosed dementia with Lewy bodies and Parkinson disease dementia. Dementia with Lewy bodies is chronic cognitive deterioration characterized by cellular... read more . Some patients develop Parkinson disease years after REM sleep behavior disorder is diagnosed.

Diagnosis of REM sleep behavior disorder may be suspected based on symptoms reported by patients or the bed partner. Polysomnography can usually confirm the diagnosis. It may detect excessive motor activity during REM; audiovisual monitoring may document abnormal body movements and vocalizations. A neurologic examination is done to rule out neurodegenerative disorders. If an abnormality is detected, CT or MRI may be done.

Treatment of REM sleep behavior disorder is with clonazepam 0.5 to 2 mg orally at bedtime. Most patients need to take the drug indefinitely to prevent recurrences; potential for tolerance or abuse is low. An alternative is melatonin 3 to 12 mg (but an optimal dosage is not known).

Bed partners should be warned about the possibility of harm and may wish to sleep in another bed until symptoms resolve. Sharp objects should be removed from the bedside.

Sleep-related leg cramps

Muscles of the calf or foot muscles often cramp during sleep in otherwise healthy middle-aged and older patients.

Diagnosis of sleep-related cramps is based on the history and lack of physical signs or disability.

Prevention includes stretching the affected muscles for several minutes before sleep. Stretching as soon as cramps occur relieves symptoms promptly and is preferable to drug treatment.

Numerous drugs (eg, quinine, calcium and magnesium supplements, diphenhydramine, benzodiazepines, mexiletine) have been used; none is likely to be effective, and adverse effects may be significant (particularly with quinine and mexiletine). Avoiding caffeine and other sympathetic stimulants may help.

Drugs Mentioned In This Article

Drug Name Select Trade
Cafcit, NoDoz, Stay Awake, Vivarin
Ceberclon , Klonopin
Diastat, Dizac, Valium, VALTOCO
Effexor, Effexor XR, Venlafaxine
Aid to Sleep, Alka-Seltzer Plus Allergy, Aller-G-Time , Altaryl, Banophen , Benadryl, Benadryl Allergy, Benadryl Allergy Children's , Benadryl Allergy Dye Free, Benadryl Allergy Kapgel, Benadryl Allergy Quick Dissolve, Benadryl Allergy Ultratab, Benadryl Children's Allergy, Benadryl Children's Allergy Fastmelt, Benadryl Children's Perfect Measure, Benadryl Itch Stopping, Ben-Tann , Children's Allergy, Compoz Nighttime Sleep Aid, Diphedryl , DIPHEN, Diphen AF , Diphenhist, DiphenMax , Dytan, ElixSure Allergy, Genahist , Geri-Dryl, Hydramine, Itch Relief , M-Dryl, Nighttime Sleep Aid, Nytol, PediaCare Children's Allergy, PediaCare Nighttime Cough, PediaClear Children's Cough, PHARBEDRYL, Q-Dryl, Quenalin , Siladryl Allergy, Silphen , Simply Sleep , Sleep Tabs, Sleepinal, Sominex, Sominex Maximum Strength, Theraflu Multi-Symptom Strip, Triaminic Allergy Thin Strip, Triaminic Cough and Runny Nose Strip, Tusstat, Unisom, Uni-Tann, Valu-Dryl , Vanamine PD, Vicks Qlearquil Nighttime Allergy Relief, Vicks ZzzQuil Nightime Sleep-Aid
NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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