Nightmare | Definition, Causes, Prevention, & Facts | Britannica (2025)

nightmare, disturbing dream that provokes a strong negative emotional reaction. Nightmares differ from other dreams in that they typically cause the sleeper to awaken because of emotional distress. An upsetting dream that does not cause the dreamer to awaken is usually not considered a nightmare. Although the causes of nightmares remain unclear, nightmare occurrence and frequency are associated with various factors, including activity level, age, diet, medication, and physical and mental health.

Characteristics

Nightmares typically occur during REM sleep, which is the deepest stage of sleep and is characterized by rapid and irregular eye movement as well as changes in breathing and heart rate. REM sleep makes up one phase of the sleep cycle (a single sleep cycle lasts about 90 to 110 minutes; most adults complete four to six cycles per night). Nightmares typically occur in the later stages of REM sleep, which may explain why they trigger the sleeper to awaken.

People can often recall their nightmares in vivid detail. This sets nightmares apart from night terrors (or sleep terrors), which involve partial awakening and are characterized by vocalizations and autonomic symptoms, such as sweating and rapid heart rate. Night terrors usually occur during non-REM sleep, the first phase of the sleep cycle.

Epidemiology

Nightmares are more common in children than in adults. It is estimated that half of children ages 3 to 6 experience nightmares and that about 20 percent of children ages 6 to 12 experience nightmares. About 50 to 85 percent of adults experience nightmares occasionally, while between 1 and 8 percent of adult sleepers experience nightmares frequently enough for the disturbing dreams to be classified as a disorder. Nightmare disorder is marked by frequent nightmares that interfere with daily life and is considered a form of parasomnia (general sleep disorder). It is more likely to develop when family members are also affected by nightmare disorder or other parasomnias.

Nightmares tend to occur at the same frequency between genders in childhood. In adulthood, however, women are more likely than men to report nightmares. In general, women’s reports about nightmares tend to center on interpersonal struggles, such as sexual harassment or attacks against family and loved ones. Men, by comparison, are more likely to report nightmares about war or terrorism.

Causes

The causes of nightmares remain unclear, though various theories have been set forth. It has been suggested, for example, that the brain uses nightmares to figure out how to respond to certain kinds of threats in waking hours; nightmares may also help the brain process stressful events that have already happened. Alternatively, nightmares may be connected to suppressed emotions; studies have found, for example, that higher levels of worry and anxiety are linked to nightmare frequency.

Environmental and lifestyle factors linked to nightmares include alcohol and drug use, disruptions in sleep schedule, illness, jet lag, periods of bereavement, and poor diet. Nightmares are most common in individuals who sleep less than 5 or more than 10 hours per night. In addition, conditions such as sleep apnea and narcolepsy are associated with nightmares, as are cancer, Parkinson disease, coronary heart disease, and chronic pain.

Nightmare occurrence is one of the main symptoms used to diagnose persons with post-traumatic stress disorder (PTSD)—an estimated 70 to 90 percent of PTSD patients experience frequent nightmares. It is thought that trauma may be a predominant cause in such instances, because PTSD nightmares are very similar to daytime flashbacks. Nightmares also generally occur at increased frequency in persons with mental health issues. For example, nightmares affect about half of all patients with borderline personality disorder (BPD) and 10 percent of those with schizophrenia. Nightmares are also linked to depression, anxiety, daytime sleepiness, irritability, insomnia, poor concentration, self-harming tendencies, and suicidal ideation.

Associations between nightmares and physical and mental health conditions may be related to increased levels of daytime stress. Nightmare occurrence and frequency may also be linked to the use of certain medications, especially amphetamines, antidepressants, antiparkinson drugs, beta-blockers, and sedative-hypnotic drugs. In particular, the use of sleep supplements, such as melatonin, and prescription sleeping drugs, such as zolpidem, are associated with the occurrence of vivid dreams and nightmares.

Nightmare prevention

Nightmares generally cannot be prevented. However, studies have shown that practicing healthy sleep habits can decrease anxiety and thus decrease the likelihood of nightmares. Avoiding caffeine, alcohol, and drugs close to bedtime and engaging in regular exercise, which decreases stress and promotes sleep quality, can also reduce nightmare risk.

In more-severe cases, imagery rehearsal therapy (IRT), a form of cognitive behavior therapy (CBT), can help reduce nightmare frequency. During IRT, patients are encouraged to reimagine their nightmares with different, happier endings. IRT and other types of CBT are used to help patients recognize their nightmares as unpleasant thought patterns, which can in turn help them to confront their fears.