“Parasomnia” is a catchall term for unusual behaviors that people experience prior to falling asleep, while asleep, or during the arousal period between sleep and wakefulness. These behaviors vary considerably in terms of characteristics, severity, and frequency.
Historically, parasomnias were considered a definitive sign of psychopathology, but some contemporary researchers argue these phenomena occur as the brain transitions in and out of sleep, as well as between rapid eye movement (REM) and non-rapid eye movement (NREM) sleep cycles. Parasomnias are more common in children than adults, but these behaviors have been recorded across different age groups.
Types of Parasomnia
While each parasomnia carries distinct symptoms and diagnostic criteria, these behaviors can be categorized into three general groups: NREM-related, REM-related, and “other.”
Non-rapid eye movement sleep constitutes the first stage of one’s sleep cycle, known as “shallow” sleep, and the second, third, and fourth stages, during which the sleep becomes gradually deeper. Collectively, these stages usually last about 90 minutes.
The most common NREM-related parasomnias are known as disorders of arousal. These parasomnias are characterized by recurrent episodes of incomplete awakening, limited responsiveness to other people attempting to intervene or redirect the sleeper, and limited cognition during the episode. Most people who experience disorders of arousal have little to no memory of their episodes. These disorders include:
- Confusional arousals: The sleeper exhibits mental confusion or confused behavior in bed. Most people who experience confusional arousals display very little autonomic arousal in the form of mydriasis (dilated pupils), tachycardia (accelerated heartbeat), tachypnea (accelerated breathing), or perspiration. Confusional arousals are also known as Elpenor syndrome.
- Sleepwalking: Also known as somnambulism, sleepwalking occurs when people get out of bed while still asleep but exhibit limited awareness or responsiveness to their surroundings. They may exhibit other complex behaviors such as sorting clothes. Sleepwalking can also lead to injuries if the individual loses their balance or collides with other objects.
- Night terrors (or sleep terrors): People who experience night terrors often scream in their sleep, though most are not responsive to outside stimuli and will have no recollection of the source for their terror upon waking. Most night terror episodes last between 30 seconds and three minutes.
- Sleep-related sexual abnormal behaviors: Known colloquially as “sexsomnia,” this specific parasomnia subtype is characterized by unusual sexual behaviors during sleep, such as aggressive masturbation, initiation of sexual intercourse, and sexual noises.
Studies have shown that males and females are equally susceptible to disorders of arousal, though age appears to play a role. Parasomnias have been reported in roughly 17% of children ages three to 13. For children and adults 15 and older, the prevalence rate falls between 2.9% and 4.2%.
Another common NREM-related parasomnia is sleep related eating disorder, which is characterized by episodes of dysfunctional eating that occur after arousal from sleep. Most people with this condition exhibit limited responsiveness during their eating episodes, and have little to no memory of the events. Hazards associated with sleep related eating disorder include ingestion of toxic substances, injuries from cooking or preparing food, and physiological effects of unhealthy or excessive eating.
Rapid eye movement sleep occurs following the first four NREM stages of the sleep cycle. Following the first complete sleep cycle, NREM and REM stages will repeat in a cyclical fashion every 90 minutes or so for the rest of the night. As the name suggests, a person’s eyes will move rapidly beneath their eyelids during REM sleep. They will also experience faster breathing, and increases in both their heart rate and blood pressure.
Common REM-related parasomnias include:
- REM sleep behavior disorder: This disorder – RSBD for short – is characterized by unusual vocalizations or movements during REM sleep, often as a reaction to a dream. It is usually attributed to dysfunction in the muscles responsible for skeletal muscle atonia, the extremely relaxed state that occurs in the REM stage. People with RSBD may undergo polysomnography examinations that record brain activity during the REM stage. This condition is most common in people aged 50 or older. Clinical findings of RSBD may be noted in patients taking certain anti-depression medications.
- Recurrent isolated sleep paralysis: People with this condition feel complete bodily atrophy during sleep onset – the period before they fall asleep – or upon waking. They will not be able to move any part of the body during these episodes, which normally don’t last more than a few minutes. Sleep paralysis can lead to anxiety or distress about falling asleep.
- Nightmare disorder: Everyone has unpleasant dreams every now and then. Nightmare disorder is limited to those who experience recurrent, vivid dreams defined by threats to survival or security that result in fatigue, distress, reduced cognition, and other daytime impairments. Nightmare disorder is a common component of Post-Traumatic Stress Disorder (PTSD). Motor activity is often limited during nightmare episodes. For children with nightmare disorder, severe psychosocial stressors are often to blame.
The “other” category for parasomnias is dedicated to behaviors that occur during the transition between sleep or wakefulness, as well as those that can occur during NREM or REM sleep. These parasomnias include:
- Exploding head syndrome: Also known as sensory sleep starts, people with this condition will hear a loud noise or feel an exploding sensation in their head when they wake up. They may also “see” an imagined flash of light upon waking. This sensation can leave the sleeper with lingering feelings of palpitation, dread, and anxiety, but it is usually painless. Some people may experience multiple episodes per night.
- Sleep related hallucinations: People with this condition experience hallucinations either during sleep onset (hypnagogic) or when they wake up (hypnopompic). These hallucinations may be visual, auditory, tactile, or kinetic in nature. In extreme cases, sleepers may leave their bed in an attempt to escape what they are experiencing. The hallucinations may persist for up to several minutes after the sleeper awakens.
- Sleep Enuresis: Known throughout the world as “bedwetting,” sleep enuresis refers to involuntary urination during sleep. Bedwetting is quite common in young children. To be considered a parasomnia, it must occur in people ages five and older and occur at least twice per week for at least three months. Primary sleep enuresis refers to people who never wake up feeling dry, while secondary sleep enuresis occurs in individuals who have not previously experienced bedwetting episodes for at least six months before the first episode occurs.
This list of parasomnias is not exhaustive, but merely reflective of the most common parasomnia types. If you believe you are experiencing a parasomnia, consult with your physician to learn about prevention tips and parasomnia treatment options.