Parasomnia is an umbrella term for any abnormal physical event or behavior (1) that occurs during different stages of sleep. While most parasomnias are not usually life-threatening, they are classified as medical disorders because they can result in physical injury, sleep loss, and adverse health effects. Parasomnias have been observed in both adults and children.
The human sleep cycle (2) consists of four stages. These include the first three stages of non-rapid eye movement (NREM) sleep, and the fourth and final stage of rapid eye movement (REM) sleep. Some parasomnias are categorized based on whether they occur during the NREM or REM stages. Other parasomnias may occur during the transitions between wakefulness and sleep.
Most NREM parasomnias are classified as disorders of arousal. These conditions occur when the sleeper is partially aroused from deep sleep without fully waking. Diagnoses for NREM parasomnias stipulate that they cannot be secondary conditions, meaning the patient does not have a psychiatric disorder, physical injury, or other medical condition that may be responsible for the parasomnia. Other diagnostic criteria for disorders of arousal include:
- Recurring events that involve an incomplete awakening from sleep
- An inappropriate response or lack of response to anyone who attempts to intervene in the parasomnia event
- Little to no cognitive recognition or dream imagery during the event
- Little to no memory of the event after it occurs
Most disorders of arousal occur during the first third of the night. Sleepers often become confused or disoriented for a few minutes after the event ends. Specific disorders of arousal include the following:
- Confusional arousals: Sleepers with confusional arousals exhibit confused behavior while partially aroused from sleep but remain in bed and do not become frightened. Their heart rate, breathing rate, and pupil dilation levels typically don’t change. Confusional arousals have been observed in roughly 17% of children (3) between the ages of 3 and 13 but are much less common for people over 15. Most people experience confusional arousal episodes during the first half of sleep.
- Sleepwalking: People who sleepwalk will physically get out of bed while partially asleep. They may display violent, belligerent, or inappropriate behavior while on the move. Sleepwalking occurs during the third NREM stage (4) and can lead to physical injury, especially if the sleepwalker is able to leave their residence. Roughly 17% of children and 4% of adults experience sleepwalking at some point.
- Sleep terrors: During sleep terrors, people who are partially aroused may scream or otherwise express extreme fear. Unlike confusional arousals, the sleeper’s heart rate and breathing rates may increase, and their pupils may become more dilated. Sweating can also occur in response to the terror. The sleeper may also attempt to physically leave their bed. Up to 6.5% of children and 2% of adults experience sleep terrors.
- Sleep-related abnormal sexual behavior: People with sleep-related abnormal sexual behavior may make unwanted sexual advances, engage in inappropriate touching, and display other sexually aggressive behaviors while partially awake. This condition is classified as a type of confusional arousal because the sleeper does not exhibit the same sexual behavior while they are awake. Still, the behavior can have unwanted social – and possibly criminal – consequences.
Additionally, sleep-related eating disorder is an NREM parasomnia that falls outside the classification for disorders of arousal. Also known as sleep eating, the condition causes people to engage in dysfunctional eating following an arousal from sleep during the NREM stage. They may attempt to eat unusual combinations of food or even toxic or inedible substances. The risk of injury and adverse health effects is fairly high. The vast majority of sleep eating patients are women, and a significant percentage have been treated or are receiving treatment for an eating disorder when their episodes occur.
REM sleep is when most dreams occur. As a result, REM parasomnias often involve responding to or acting on dreams. The most common REM parasomnias include:
- REM sleep behavior disorder (RBD): People with RBD often make profane statements, punch or kick their partner, or otherwise become aggressive in their sleep. These behaviors are believed to occur as a response to unpleasant dreams, and the sleeper may partially or fully remember their behavior upon waking.
- Recurrent isolated sleep paralysis: Also known as hypnagogic paralysis, this condition causes an inability to move the body or limbs when falling asleep or waking. These episodes may last anywhere from a few seconds to several minutes. People with recurrent isolated sleep paralysis may develop sleep anxiety as a result. Predisposing factors include sleep deprivation and an irregular sleep schedule.
- Nightmare disorder: Everyone has bad dreams every now and then, but nightmare disorder is linked to recurring, vividly unpleasant or frightening dreams with lingering psychological and cognitive after-effects. People with nightmare disorder often feel fatigued or sleepy the next day, struggle with concentration and memory, and display poor performance at school or work. Nightmare disorder is quite common in young children, affecting up to 50% of those between the ages of 3 and 6.
Some parasomnias occur during the transitional period between sleep and wakefulness, rather than during specific stages of the sleep cycle. These parasomnias include:
- Exploding head syndrome: As the name implies, this parasomnia causes people to feel as though their head is literally exploding as they fall asleep or wake up during the night. A loud, imagined popping or banging sound often precedes the “explosion.” Exploding head syndrome can cause distress, but is not associated with any physical pain.
- Sleep-related hallucinations: People with this condition experience recurring hallucinations immediately before falling asleep or waking up in the night. These hallucinations are mostly visual in nature, but may also involve auditory, tactile, or kinetic elements. People who report sleep-related hallucinations may also experience other parasomnias, such as sleep paralysis or sleepwalking.
- Sleep enuresis: Sleep enuresis, or bed-wetting, consists of involuntary urination during sleep. Bed-wetting is most common in children, but can also affect adults. In order to receive a diagnosis for sleep enuresis, patients must be at least 5 years old and experience two or more weekly episodes for at least three months.
Parasomnias are not always primary conditions. These disorders may occur due to a medical disorder, medication, or consumption of certain substances. For example, RBD often occurs in tandem with degenerative medical conditions such as Parkinson syndrome, multiple system atrophy, and dementia with Lewy bodies. The sedative-hypnotic medication Zolpidem – sold under the name Ambien – has also been linked to sleep eating, sleep driving, and other NREM parasomnias.
In other cases, patients may receive a “parasomnia, unspecified” diagnosis if their physician suspects a parasomnia but cannot pinpoint a recognized disorder based on the patient’s symptoms. This can also occur due to an underlying medical condition that causes parasomnia-like behavior.
Lastly, sleep talking is considered a parasomnia that appears to affect most of the population. Sleep talking can occur in NREM sleep, REM sleep, or transitional phases. There are no major complications associated with sleep talking, though loud or offensive vocalizations could potentially create problems for the speaker.
The best treatment for parasomnias depends on the patient’s specific diagnosis, age, and severity of symptoms. Parasomnias that largely affect children, such as sleep terrors, sleepwalking, confusional arousals, and nightmare disorder often resolve on their own without any medical intervention. Bedroom or home safety counseling may also be effective. For sleepwalking, treatment may not be needed unless a physical injury occurs.
Other parasomnias may be treated using medication. For example, low doses of the sedative clonazepam are often prescribed for people with RBD. These patients may also alleviate their symptoms with melatonin supplements. Anyone who struggles with a parasomnia should speak to their doctor before taking any sort of medication to alleviate their symptoms.
- American Academy of Sleep Medicine. (2014). The International Classification of Sleep Disorders – Third Edition (ICSD-3). Darien, IL. https://aasm.org/
- National Institute of Neurological Disorders and Stroke. (2019, August 13). Brain basics: Understanding sleep. Retrieved April 15, 2022, from https://www.ninds.nih.gov/Disorders/patient-caregiver-education/understanding-sleep
- Carter, K. A., Hathaway, N. E., & Lettieri, C. F. (2014). Common sleep disorders in children. American Family Physician, 89(5), 368–377. https://pubmed.ncbi.nlm.nih.gov/24695508/
- Schwab, R. J. (2020, June). Parasomnias. Merck Manual Consumer Version. Retrieved April 20, 2022, from https://www.merckmanuals.com/home/brain,-spinal-cord,-and-nerve-disorders/sleep-disorders/parasomnias