What is considered a nightmare?

Clinicians concerned that a patient may have a problem such as sleep paralysis, sleep terrors, or nightmare disorder should know that many patients do not have the language to describe or differentiate these experiences. As a result, they may refer to any of them simply as nightmares, said Antonio Zadra, PhD, a psychology professor at the University of Montreal. “These disorders and their treatments are very different. If a patient reports having nightmares, some basic questioning is warranted,” he said.

[Related: The science of nightmares]

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The distinction between a bad dream and a nightmare is quite subjective, but some researchers describe bad dreams as moderately distressing dreams that do not cause the dreamer to wake up.

Some researchers define nightmares as distressing dreams that cause a person to awaken because of their frightening imagery or the emotions they evoke. They tend to be elaborate and well-remembered. Nightmares usually occur during rapid eye movement (REM) sleep, typically in the second half of the night. Nightmares are most frequent between ages 6 and 10, but occasional ones are common in people of all ages.

Nightmares are common after a trauma, affecting up to 70% of people with posttraumatic stress disorder (PTSD). They often closely replicate traumatic events. Unlike nontraumatic nightmares, they occur across all stages of sleep, not just during REM sleep.

Some researchers have begun studying “complex” nightmares, which they define as trauma-related nightmares that coexist with sleep apnea. When their sleep architecture is disturbed by disordered breathing, someone with complex nightmares may be less likely to remember the content of those dreams.

These are sleep disorders, or parasomnias, which occur during slow-wave non-REM sleep, usually in the first half of the night. Unlike nightmares, they do not contain elaborate dream scenes. People often wake screaming from sleep terrors but have no memory of the event the next morning. Sleep terrors tend to peak in children 3 to 7 years old.

Sleep paralysis occurs when a person becomes conscious while still transitioning from sleep to wakefulness. The person is unable to move for seconds or minutes and may feel panic, pressure, or a sensation of suffocating. Sleep paralysis is thought to be related to a disturbed REM cycle and is estimated to affect about 8% of the general population and nearly a third of psychiatric patients (Sharpless, B. A., & Barber, J. P., Sleep Medicine Reviews, Vol. 15, No. 5, 2011opens in new window).