The Mystery of Night Terrors
What we know, and don't yet know, about the phenomenon.
Posted Mar 30, 2015
Stephanie had just fallen asleep when suddenly she was torn from slumber by the screams of her youngest daughter, Maddy. She jumped from her bed and ran to her daughter’s room, alarmed by the frightening sound of her wild howls. She found her daughter sitting bolt upright in bed, shrieking at the top of her lungs, inconsolable. Stephanie’s husband and other children were now awake and unsettled, almost as if emerging from a nightmare themselves. After what seemed like a very long time Maddy gradually fell back asleep. Stephanie was shaken and all the others were awake and worried. The next morning, Maddy awoke and seemed perfectly fine—with no apparent memory of the night before.
The episode seemed inexplicable, but there is a scientific explanation behind it.
The above vignette has all of the signs of a non-REM (NREM) sleep parasomnia. The International Classification of Sleep Disorders (AASM, 2014) defines a parasomnia as “undesirable physical events or experiences that occur during entry into sleep, within sleep, or during arousal from sleep.” These events can occur in the transition from sleep to wakefulness, from wakefulness into sleep, during deep sleep and in REM sleep. They may involve complex behaviors, unusual perceptions, powerful emotions and strong physiological experiences such as flight or fight responses. These events occur during sleep state dissociations during which several states of consciousness are present at the same time. For example, a person may, in effect, be both awake and asleep at the same time.
In the case of Stephanie’s daughter, dissociation occurred such that aspects of both wakefulness and NREM sleep were present at the same time. Had this taken place while her daughter was being monitored during polysomnography, it would have shown an EEG pattern of NREM sleep with muscle activity as in wakefulness also present. Because the reasoning centers of the brain are asleep, it is nearly impossible to console a child or adult who is having this type of parasomnia, known as a sleep terror.
The most common time for sleep terror to occur is during the first third of the night when the greatest depth of sleep occurs. It usually starts with a frightening vocalization, most often a scream. The person often sits bolt upright and appears to be in a state of great fear with rapid heart rate, rapid breathing, tense muscles and sweating. There may also be incoherent verbalizations. The eyes are usually open but the person appears confused and is non-responsive.
These events usually last only a few minutes but can go on as long as half a hour or so and may be very upsetting to any witnesses. Usually the child or adult will just fall back asleep, but if awakened, will appear confused and disoriented. Rarely, an adult will actually leave bed and run away. At this point the sleep terror has turned into an episode of sleepwalking. This is dangerous as violent behaviors can occur if efforts are made to stop the person from leaving. Injury can also occur if the person falls or trips over objects in the environment. Adults may on occasion recall fragmentary dream imagery from the experience; most often, however, both children and adults have no memory of the event and no other daytime effects, unless injury has occurred.
Sleep terrors are equally prevalent for males and females and are most common in children and adults 35 years of age or younger. Prevalence rates may be as high as 6.5 percent in children. Prevalence in adults is around 2.3 percent, and only about 1 percent in older adults aged 65 or older.
Sleep terrors can be frightening for those awakened by the sleeper’s screams, but thankfully they are relatively infrequent among those who have them and usually cause little harm. In the case of infrequent events in which the individual remains in bed, a professional’s reassurance is often all that is needed. If they occur with greater frequency or involve dangerous behaviors as when the sleep terror transitions into sleep walking and includes injury to self or others, treatment is warranted.
I will discuss the treatment of parasomnias in a future post.
American Academy of Sleep Medicine. (2014). International classification of sleep disorders, 3rd ed. Darien, IL: American Academy of Sleep Medicine.