What Are Night Terrors?

Almost everybody has witnessed a night terror in a child, a spouse, a roommate, or a friend, but the precise definition of the condition known in the medical literature as pavor nocturnus requires a reference to the four stages of sleep.

In a night terror, the sleeper awakens suddenly from stage 4 sleep, usually with screaming, shouting, moaning, or groaning, and then settles back to sleep without fully awakening. Stage 4 is the deepest, most regenerative phase of sleep.

In stage 1 sleep, the eyes might roll slowly while the mind wanders. Body temperature and pulse rate both fall.

In stage 2 sleep, the eyes are quite, and the sleeper may begin to snore as airway resistance increases. Dreams during stage 2 sleep are usually recalled in vague terms.

In stage 3 sleep, it takes a really loud sound to wake up the sleeper. There is further slowing of the metabolism and lowering of body temperature, respirations, and pulse, and the pituitary begins to secrete growth hormone to repair and rejuvenate tissues.

In stage 4 sleep, it is almost impossible to wake the sleeper. Pulse and temperature are at their lowest levels of the night, and growth hormone is at maximal production. Night terrors occur in stage 4 sleep.

And in REM or rapid eye movement sleep, the heart rate is about 5 per cent faster than in the other stages of sleep, and there may be vivid dream recall. If the sleeper is dreaming about a sound, it is harder to awaken him or her.

Not everybody goes through the stages of sleep at the same time, but most sufferers of night terrors go into stage 4 sleep and are susceptible to night terrors 45 to 90 minutes after going to bed. It is almost as if the brain cannot quite go into REM, so tensions build up and the night terror results.

Children, in particular, but also adults who have night terrors often cannot recall them. The mind is usually "blank" during the deeper stages of sleep when night terrors are absent, but a person who has night terrors may site up in bed for five minutes to half an hour while the heart races 160 to 180 beats a minute, pounding as hard as during intense exercise. The next morning there may be a vague recollection of a shadowy, threatening person or animal (such as snakes and spiders), but often there's no memory of the event at all.

There are several things a night terror is not:

• A night terror is not a sign of mental illness, especially in children. (Adults with night terrors tend to have suffered traumatic stress.)
• A night terror is not proof of physical abuse.
• Night terrors usually are not caused by watching scary movies or listening to arguments, although these kinds of emotional stresses may cause insomnia.

And there are several ways to distinguish night terrors from other common sleep disturbances:

• Nightmares are remembered. Night terrors are not.
• In small children, nightmares usually occur between 4 and 6 am. Night terrors usually occur between 1 and 3 am.
• A child who has had a nightmare will respond to comforting. A child who has had a night terror usually will not.
• Nightmares occur during REM sleep. Night terrors occur during deep sleep.
• Seizures begin and end much more quickly (usually in less than 2 minutes) than either nightmares or night terrors (up to 30 minutes). Seizures can have an explosive onset and an equally abrupt offset.
• Nightmares usually are not associated with labored breathing or racing heart. Night terrors are usually associated with both labored breathing and racing heart.

The causes of night terrors are as murky as the condition itself, but low blood sugars (hypoglycemia), use of certain antidepressant medications, and genetics may all play a role. And because people who experience night terrors do not have an accompanying dream, they usually do not remember them. It is OK to tell adults they have night terrors, but it is usually not a good idea to tell little children.

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