A night terror is not a bad dream, and the sleeper rarely remembers it
A child sits bolt upright a couple of hours after falling asleep, eyes wide, screaming, heart racing, unable to recognise the parent at the bedside. Minutes later the child is asleep again, and by morning remembers nothing. That is a night terror, and it comes from a different stage of sleep than nightmares do.
Nightmares happen during rapid eye movement sleep, the dreaming phase that dominates later in the night. People usually wake from them fully, remember the story vividly, and seldom shout or thrash. Night terrors strike instead during an incomplete arousal from deep slow-wave sleep, which is concentrated in the first part of the night. The brain is caught between states: the body mounts a full alarm response while awareness stays switched off. Until scientists began studying rapid eye movement, there was no way to tell the two experiences apart.
The episode itself is dramatic. Typical signs include a wide-eyed look of fear, incomprehensible yelling, sweating, flushed skin, dilated pupils, fast shallow breathing and a heart rate that can double. Some people kick, flail or leap out of bed as if escaping danger, and sleepwalking often accompanies an attack because both belong to the same family of deep-sleep disturbances. The defining feature is that the person cannot be comforted. An episode usually lasts between one and ten minutes, sometimes longer in children.
Young children are by far the most affected. Estimates suggest more than a third of toddlers have had an episode by 18 months and about a fifth by 30 months, while only a few percent of adults do. Onset often peaks around three and a half, and most children simply outgrow them. In children, attacks carry no link to psychiatric illness; in adults the picture differs, with stronger ties to anxiety, trauma and other conditions.
The tendency runs in families. Relatives of people with night terrors are markedly more likely to have them, and identical twins share them more often than fraternal twins. Triggers that make episodes likelier include sleep deprivation, fever and stress. They are also stubborn to study, since they tend to occur less often in a sleep laboratory than at home.
Source: Night terror
