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Harvard Commentaries
Harvard Commentaries
Reviewed by the Faculty of Harvard Medical School

Minding Your Mind Minding Your Mind

Nightmares and Other Sleep Disturbances

March 20, 2013

By Michael Craig Miller M.D.

Harvard Medical School

"Sweet dreams."

It's a common way to say goodnight. And pleasant dreams often accompany a good night's sleep. But sleep isn't always sweet.

Some people have bizarre behaviors or really bad dreams during sleep. These can lead to accidents or violence. Nightmares may even trigger heart attacks.

These experiences are related to a group of disorders called parasomnias. They are different from insomnia (the inability to fall asleep or maintain a restful sleep) and hypersomnia (excessive daytime sleepiness that's usually caused by poor sleep at night).

Some parasomnias are rare and others are more common in children than adults. But they can also strike grown men, sometimes causing injuries or other problems. Here's a look at these disorders.

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Sleep Walking

Sleepwalking, or somnambulism, is often the target of stand-up comics, but it's no joke for people affected by this relatively common problem. Although sleepwalking is most common in children, it can occur at any time in life.

The episodes usually begin within 15 minutes to two hours of falling asleep. Although the sleepwalker may have his eyes open, he has an unfocused, glassy stare and does not respond to someone talking to him.

Sleepwalking involves much more than walking. Sleepwalkers can carry objects, eat, rearrange clothing or furniture, urinate in inappropriate locations, go outdoors and even drive.

The potential for harm is obvious. A sleepwalker can also injure others with violent, even homicidal behavior. Fortunately, violence during sleepwalking is rare.

Episodes of sleepwalking are usually brief and are over in less than 10 minutes. Most sleepwalkers continue sleeping and have either no memory of the episode or a vague, dreamlike recollection.

Sleepwalking can run in families, but doctors don't understand what causes the disorder. If episodes seem to be triggered by sleep deprivation, stress or a medical illness, therapy is directed at the underlying problem. Unfortunately, though, there is no well-established treatment for sleepwalking itself.

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Sleep Terrors

Like sleepwalking, sleep terrors — also known as night terrors — are classified as partial arousal disorders. The sufferer remains asleep but may look or sound alert. Sleep terrors usually occur in children; the problem often runs in families.

An episode begins abruptly with a piercing, loud scream of intense fear. Although the screamer remains asleep, he typically sits up in bed and appears agitated, even frenzied. Rapid breathing and a racing heart are common.

The pupils of the eyes may look wide with fright. Despite his apparent terror, the sufferer does not remember any frightening thoughts. Because sleep terrors lack dream content, they are quite different from nightmares. The episodes are brief, and most children outgrow the attacks. Antidepressants or sedatives can sometimes provide short-term relief.

Sleep-Related Eating Disorders

Many people like to snack at night. But for some, eating at night is not a conscious choice or a guilty pleasure. Eating during sleep or partial arousal from sleep is involuntary, uncontrollable and often bizarre.

Night-eating syndrome can begin any time in life. But it's most common in young adults and it's more common in women than men. Some night eaters also suffer from other sleep disorders, such as sleepwalking and restless legs syndrome, but in others night eating is the only problem.

Episodes occur on most nights. Night eaters typically consume high-calorie food, and some ingest bizarre items ranging from raw meat to cat food. Night eaters complain of morning bloating, loss of appetite, and — no surprise — weight gain. Still, they usually have little or no memory of their nighttime eating binges. Counseling is not effective, but antidepressants and possibly melatonin may help.


Nightmares can be as upsetting as night terrors and may sometimes have serious medical consequences.

Dreaming can occur during all stages of sleep. Dreams that develop during non-rapid eye movement (NREM) sleep tend to be short, simple and vague. In contrast, rapid eye movement (REM) sleep usually gives rise to dreams that are intricate and detailed, with plotlines and associations that are often bizarre.

To psychologists, dreams express emotional processes and mental stress. But for sleep scientists, a dream is simply mental activity during sleep that is remembered after awakening.

Both pleasant dreams and nightmares occur primarily toward morning when REM sleep is most concentrated.

Nightmares are common; at any one time, five to eight percent of adults report them. They often strike perfectly healthy people for no clear reason, but they can also result from medications (antidepressants, beta-blockers, anti-Parkinson's drugs, cholesterol-lowering medications, and testosterone blockers used for prostate cancer), psychiatric illnesses, or during withdrawal from alcohol or sedatives. Nightmares are particularly frequent and troublesome in people with post-traumatic stress disorder (PTSD).

Nightmares usually waken people from sleep, and they often boost the heart rate and blood pressure. If people can get back to sleep, a nightmare is little more than a bad dream. But recurrent nightmares can lead to unrestful, fragmented sleep that interferes with normal daytime functioning.

People who are troubled by nightmares may benefit from changes in medication or treatment of underlying problems, such as anxiety disorders or PTSD. But for some individuals, a nightmare can produce a major threat to health.

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The Link Between Nightmares and the Heart

Although heart attacks seem to strike out of the blue, many are actually triggered by particular events or experiences. Vigorous exercise, such as snow shoveling, and intense emotions, particularly anger, are well-known examples. One thing these triggers have in common is a surge in the stress hormone adrenaline, which sets the heart racing and the blood pressure soaring.

Nightmares are most common in the pre-dawn hours. They often wake up the dreamer with a jolt of fear. And nightmares pour adrenaline into the blood, boosting the heart rate and blood pressure, and activating the blood clotting system. Perhaps that's why scientists in Turkey reported a link between nightmares and heart attacks that strike during sleep.

For most men, a heart attack is a nightmare; for some, a nightmare can trigger a heart attack.

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