A dream is the recall of mental activity that has occurred during sleep. Using polysomnography, sleep can be divided into stage 1 (sleep onset), stage 2 (light sleep) and stages 3 and 4 (deep sleep)—the non–rapid-eye-movement (REM) stages. REM sleep occurs cyclically every 90 minutes during the night in association with high brain activity, rapid spontaneous eye movements and suppressed voluntary motor activity. Dreaming occurs in all stages of sleep. It is reported by 80 percent of persons who are awakened during REM sleep and sleep onset (stages 1 and 2), and 40 percent of persons who are awakened from a deep sleep.

Patient reports about the content of their dreams vary based on the sleep stage from which they are awakened. Patient reports of dreams experienced during REM sleep tend to be bizarre and detailed, with storyline plot associations. In contrast, dreams experienced in deep sleep are more diffuse (e.g., dreams about a color or an emotion). The dreams of stages 1 and 2 are simpler, shorter and have fewer associations than the dreams of REM sleep. The ability to recall dreams may reflect the dream's accessibility or distance from awake thought; the highest recall seems to occur during sleep stages with electroencephalographic patterns that are most like those in the waking state.¹

Some researchers believe that dreams have no function. Others think that dreams are the nocturnal continuation of conscious thought processing during the day or a reprogramming of the central nervous system for the next day's conscious functioning.² Evidence suggests that dreaming, like most other physiologic events, is important for learning and memory processing, gives cognitive feedback about a person's mental functioning and helps a person adapt to emotional and physical stress.³

Frightening Dreams: The Nightmare

Nightmares are vivid and terrifying nocturnal episodes in which the dreamer is abruptly awakened from sleep. Typically, the dreamer wakes from REM sleep and is able to describe a detailed, associative, often bizarre dream plot. Usually, the dreamer has difficulty returning to sleep. Nightmares are also common. In a two-week prospective study of college students, 47 percent described having at least one nightmare.⁴ Results of a general population study of 1,049 persons with insomnia revealed that 18.3 percent had nightmares.⁵ In this study, nightmares were more common in women and were associated with increases in nocturnal awakenings, sleep onset insomnia, and daytime memory impairment and anxiety following poor nocturnal sleep.⁵ Studies of the general population reveal that 5 to 8 percent of the adult population report a current problem with nightmares (Table 1).^6,7

Nightmares affect 20 to 39 percent of children between five and 12 years of age.⁸ Contrary to popular belief, frequent nightmares in children do not suggest underlying psychopathology. Nightmares are often described by creative persons who demonstrate “thin boundaries” on psychologic tests.⁹ Persons with thin boundaries are less likely than others to define the world around them in concrete terms. They rarely define issues as being black and white, but instead see themselves and the world in shades of gray.¹⁰

Nightmares are also associated with the use of medication, primarily those medications that affect neurotransmitter levels of the central nervous system, such as antidepressants, narcotics or barbiturates. Intense, frightening dreams may occur during the withdrawal of drugs that cause REM sleep rebound, such as ethanol, barbiturates and benzodiazepines (Table 2).¹¹

Nightmares and Post-traumatic Stress Disorder

Nightmares are a defining symptom in post-traumatic stress disorder (PTSD).^12,13 The latter is not a new disorder. In 1667, after the great fire of London, Samuel Pepys wrote, “To this very day I cannot sleep a-night without great terrors of the fire.” Nightmares related to PTSD occur after an intensely frightening or highly emotional experience. These nightmares are often associated with disturbed sleep and altered daytime behavior, which is best described as hyperarousability.^14,15

The occurrence of PTSD following trauma varies. Thirty percent of veterans of the Vietnam War were affected by PTSD, as were 68 percent of veterans who were in the Arab-Israeli conflict of 1973 and 8 percent of veterans of the Gulf War.¹⁶ Among the civilian population, PTSD affects approximately 25 percent of persons who have experienced emotional and physical trauma or have suffered a severe medical illness. However, among some groups of patients, such as immigrant psychiatric patients, the incidence of PTSD approaches 40 percent.^17–21

The frequency of PTSD increases with severity of trauma, hostility, depression, poor health habits and poor coping skills. Persons with PTSD generally report awakening from dreams that involve reliving the trauma. In these dreams, they experience strong emotions, such as rage, intense fear or grief, that would have been appropriate reactions to the original traumatic event. Nightmares related to PTSD generally happen during REM sleep but also occur at sleep onset, which can interfere with the initiation of sleep.¹² Polysomnographic studies in these patients have shown that they have poor sleep maintenance, increased eye movement density, decreased percentage of REM sleep and an increased tendency to have REM sleep at sleep onset (REM pressure). This phenomenon is similar to that occurring in patients with narcolepsy.²²

Symptoms of PTSD can persist for decades after the traumatic experience; however, the occurrence of PTSD after trauma is the exception rather than the rule.²⁰ Patients who experience PTSD are divided into two groups based on the presence or absence of impaired psychologic functioning before the trauma.¹⁶

Nightmares and Psychiatric Illness

Nightmares can occur in patients with psychiatric illness. Depression is sometimes associated with themes of masochism and poor self-image in dreams.^23,24 Patients with schizophrenia and dissociative disorders may have intense dreams during a relapse of the illness. Panic attacks can occur during REM sleep in patients who have panic disorders and depression, and in patients who have asthma and breathing disorders of sleep. The REM sleep rebound related to withdrawal from alcohol and sedative-hypnotics, which chronically suppress REM sleep, may present as disturbing nightmares.²⁵

REM-Sleep–Associated Disorders

A strong association exists between REM sleep and dreaming. Most frightening dreams occur during REM sleep, and most REM-altering disorders and medications affect dreaming. A variety of REM-associated parasomnias can alter dreaming (Table 3).²⁵ Symptoms of underlying illness can also occur during REM sleep (Table 4).²⁵ It often happens that persons awakening from REM sleep, a state that is electrophysiologically near waking, recall the mentation and physical symptoms associated with the state of REM sleep.

REM Behavior Disorder

REM behavior disorder most commonly affects middle-aged men. Patients with this disorder often present with a history of sleep-associated injuries to themselves or a sleeping partner. REM behavior disorder is characterized by vivid, action-filled, violent dreams that the dreamer acts out, sometimes resulting in injury to the dreamer or the sleeping partner.¹⁸ On polysomnography, these patients show elevated submental and limb electromyographic tone, which may be phasic or tonic and that is associated with prominent jerking of the limb or truncal areas.²⁶

REM behavior disorder often occurs without concomittant pathophysiology, but can be associated with neurodegenerative neurologic disorders. The most common of these disorders are Parkinson's disease, primary dementia and narcolepsy.¹⁸ Computed tomography or magnetic resonance imaging brain scans of affected patients may show diffuse hemispheric lesions, bilateral thalamic abnormalities or brain stem lesions.²⁵

Night Terrors

Night terrors are nocturnal episodes of extreme terror and panic that usually occur early in the sleep period.¹⁰ They are similar to other arousal disorders that occur during deep sleep, such as somnambulism (sleepwalking) and confusional arousals. Night terrors are associated with autonomic discharge, confusion and vocalizations, often a “blood-curdling” scream. Persons with night terrors are often difficult to arouse and have limited recall of their dream content.²⁷ Night terrors can occur in association with the other arousal disorders that are associated with deep sleep (Table 3).²⁵ Night terrors are most common in children between four and 12 years of age and affect 1 to 4 percent of the population.^25,28 Polysomnographic studies in these patients generally show increased arousals from deep sleep.²⁹

Adults who have night terrors are more likely than children to have psychopathology, mainly substance abuse and affective disorders.²⁹ As with other parasomnias that affect adults, night terrors are more likely to occur in association with other sleep pathology, such as periodic limb movements and obstructive sleep apnea.³⁰

Diagnostic Testing

Often, nightmares and night terrors can be diagnosed on the basis of the patient's history. In persons who have a history of nocturnal injuries, polysomnography is required to diagnose REM behavior disorder or nocturnal seizures. To diagnose REM behavior disorder, the use of additional electromyographic arm leads is required. In up to 25 percent of patients with epilepsy, the condition may present only as nocturnal seizures.²⁵ A diagnosis of nocturnal seizure may be suggested by family history, stereotypic nocturnal behaviors and incontinence. Nocturnal seizures can be grand mal, petit mal, partial-complex, vegetative or paroxysmal nocturnal dystonias.²⁵

All parasomnias more commonly affect persons who have breathing disorders during sleep. Polysomnography is appropriate for any patient with symptoms or signs of obstructive sleep apnea, such as daytime hypersomnolence, nocturnal hypoxia, loud snoring and increased neck circumference. REM behavior disorder often occurs concomitantly with degenerative neurologic illnesses that may require further evaluation. In adults, the onset of arousal disorders such as somnambulism and night terrors may reflect underlying neurologic disease. Thus, neurologic evaluation, including imaging of the central nervous system, may be indicated.

Treatment

NIGHTMARES AND NIGHT TERRORS IN CHILDREN

Nightmares and night terrors in children are usually disturbing to parents and family members; therefore, proper diagnosis and education of family members are important components of management. It is essential to control the environment by removing dangerous objects and providing barriers to prevent escape from a safe sleeping environment. Reassurance and support are often the only therapy required because these disorders rarely, if ever, reflect underlying illness and usually disappear with maturity. Pharmacologic intervention is not usually indicated; in fact, it should be discouraged because it may contribute to further sleep disruption.²⁸ Behavioral methods for treatment of frequent nightmares are effective in older children.

REM BEHAVIOR DISORDER

Clonazepam (Klonopin), in a dosage of 0.5 to 1.0 mg at bedtime, is generally effective in the treatment of REM behavior disorder. Long-term efficacy and safety have been reported, along with relapse when the medication is discontinued.¹⁸ Response to other medications (primarily antidepressants) has been reported with postulated effects secondary to diminished REM sleep.³¹ Many parasomnias in adults, including night terrors, respond to this pharmacologic approach.

POST-TRAUMATIC STRESS DISORDER

PTSD can be a short-term, limited problem or a lifelong, chronic illness that results in recurrent hospitalizations, impaired social relationships and aggressive or self-destructive behavior. Although many different approaches to treatment have had limited success, psychotherapy, individually or in a group setting, is generally indicated and can help with resocialization. Cognitive restructuring, eye movement desensitization and reprocessing therapy, prolonged exposure (flooding) therapy and nightmare imagery techniques can decrease symptoms in patients with PTSD for months after therapy.^32,33 Fluoxetine (Prozac) is an effective agent in the treatment of symptoms of PTSD.³⁴ This condition is often associated with anxiety and mood disturbance, which may also require pharmacotherapy.

RECURRENT NIGHTMARES

Nightmares that occur after the patient has experienced trauma or stress may lead to an interpersonal integration of the event. On the other hand, long-term persistence (the habitual pattern of recurrent nightmares not associated with recent trauma) can cause a decline in daytime functioning without apparent benefit.

Behavioral approaches in the treatment of nightmares have been successful and can result in short- and long-term reduction of nightmare frequency in more than 70 percent of patients. Such therapy requires only a few group or individual sessions with a psychologist or in a sleep medicine center.^32,33