Parasomnias are disruptive sleep-related behaviors that occur during or surrounding sleep. They can include abnormal movements (such as sleep walking or acting out dreams) or distressing dream content (nightmare disorder). With these disorders, sleep environment safety is vital to prevent injury.


Parasomnia behaviors can emerge from non-rapid eye movement (NREM) sleep or rapid eye movement sleep (REM) also known as dream sleep.

NREM parasomnias are disorders of arousal. These behaviors occur during deep sleep (stage 3) and typically affect the first half of the night. People with NREM parasomnias often have no recollection of, or only vaguely recall, these episodes. Episodes consist of complex movements and behaviors that may appear semi-purposeful. REM-related parasomnias occur during REM sleep (dream sleep) and typically affect the second half of the night.


  • Isolated sleep paralysis: Loss of muscle tone and temporary muscle paralysis are normal during REM sleep. This phenomenon may be frightening and can last for a few seconds to minutes when an individual wakes up. Occasional sleep paralysis isn’t unusual with sleep deprivation being a common trigger.
  • Sleepwalking (Somnambulism): Sleepwalking is characterized by complex, sometimes semi-purposeful activity that arises during Stage 3 sleep. The affected person may sit up in bed or get up and walk around, occasionally sustaining an injury. Upon waking up, the patient usually has no recollection of what occurred. Sleepwalking can be normal in children but should be evaluated if it emerges in adults. Sleep-related eating disorder is a variant of sleep walking and is characterized by recurrent episodes of involuntary eating during an arousal from sleep. Usually, the affected individual has a diminished level of consciousness or awareness of this behavior.
  • Sleep terrors: Sleep terrors are characterized by the affected individual screaming during sleep, often with elevated heart rate, dilated pupils, and sweating. Upon questioning, they commonly describe feeling intense fear rather than detailing the specifics of a dream. Sleep terrors arise during Stage 3 sleep and are most likely to occur during the first hour or two. Sleep terrors can be normal in children but should be evaluated if they emerge in adults.
  • REM behavior disorder: REM sleep behavior disorder is characterized by episodes of acting out dream content. Typically occurring in the second half of the night, people with REM sleep behavior disorder mumble, talk, or laugh during sleep, and move their arms or legs in what appears to be semi-purposeful movements (running or hitting/punching). Diagnosis and treatment are critical because REM behavior disorder with dream enactment can result in injury.
  • Nightmare disorder: Nightmare disorder is characterized by the presence of frequent distressing dreams. Patients often recall details of their dreams and find them distressing after waking or feel that the dreams impact their ability to get a good night’s sleep.
  • Nocturnal epilepsy: Seizures can sometimes manifest during sleep. Associated movements are usually repetitive and leave the affected individual disoriented or confused. Because the movements can be difficult to capture and diagnose, patients with suspected nocturnal epilepsy may require long-term monitoring.


Though the diagnosis of parasomnias is largely based on clinical history, many adults with symptoms of parasomnias participate in in-lab overnight sleep studies to evaluate any underlying triggers for their behavior. In the case of dream enactment, this study can identify the presence of REM sleep without normal loss of muscle tone.


Treatment depends on the specific parasomnia identified and the degree to which it disrupts sleep. A critical component of treating parasomnias is consideration of sleep environment safety. Depending on symptoms, this may include the use of bed alarms, moving furniture away from the bed and placing a mat on the floor, or sleeping alone.

Sleep Disorders Center

The Sleep Disorders Center at BIDMC is one of the largest academic sleep centers in New England. This multi-disciplinary center includes neurologists, pulmonologists and psychologists who treat adult patients with the full range of sleep disorders, ranging from sleep apnea to insomnia, narcolepsy to restless leg syndrome.

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