Unusual nighttime events such as night terrors, sleep talking, or sleepwalking are known as parasomnias. They are mostly harmless, always intriguing, occasionally humorous and often scary. For sleep scientists they represent a very interesting series of naturally-occurring experiments at the boundaries between human states: wakefulness, non-REM sleep and REM sleep. These weird amalgams and overlaps of states cannot always be explained, but they reveal aspects of sleep that could not otherwise be observed.
Non-REM (or Arousal) Parasomnias
Night terrors, sleep talking, and sleepwalking originate in deep sleep, usually during the first third of the night. They occur more frequently in childhood and decrease with age, though a small percentage of adults still experience these events. There appears to be a genetic link to the phenomenon; and scientists have never found an underlying pathology. Treatment is typically not needed unless the episodes are frequent and interfere with the night routines of people who sleep in the vicinity.
In some cases, an overnight sleep study may be prudent to rule out epileptic seizures at night.
As a practical matter, the sleeping environment for someone who experiences parasomnias must be prepared in such a way as to prevent physical injury during episodes – essentially “parasomnia-proofed”, for lack of a better term.
Children experience night terrors frequently, as many parents well know. They scream, cry, become agitated and frightened, and are inconsolable. Any attempt to wake or comfort them makes things worse. There is no actual disruption of sleep; and they retain no memories of dreamlike experiences when they wake at the end of an episode. They may, however, feel and express fear without a specific reason.
Sleep talking and sleepwalking involve complex motor behavior, but represent two extremes on the activity continuum. Talking obviously involves relatively little movement; but sleepwalking is a very agitated state. In spite of that, sleepwalkers rarely leave their abodes. They retain no memory of the event; and there is no disruption of sleep. Treatment is not required for infrequent episodes, but the sleep environment must be made safe.
Episodes start in late childhood and typically stop by the late teens. For an unfortunate few, the episodes persist into adulthood.
REM Sleep Parasomnias
Nightmares are simply bad dreams. They occur mostly in the last part of the night when REM sleep predominates, whereas sleep terrors intrude into the first part of the night. When people wake after a nightmare they can provide a detailed report of the frightful experience.
Sleep paralysis occurs when one wakes up suddenly from REM sleep but is unable to move because REM-related muscle inhibition is still in place temporarily. Though frightening, it’s a harmless phenomenon. The problem may occur sporadically without a known cause; or it may recur within family clusters. In many cases it’s an isolated event, but it can also occur as a symptom of narcolepsy.
REM behavioral disorder presents with agitated motor activity during REM sleep that can put sufferers or their bed partners at risk for injury. This happens when normal muscle inactivation during REM sleep disappears, thus causing apparent violent behavior while sleeping. An overnight sleep study can diagnose the disorder easily. An underlying brain or neurological problem causes this, and sometimes precedes Parkinson’s disease by many years.
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