A mother is awakened in the middle of the night by a terrifying scream. She races to the room of her three-year-old son, who is sitting up in bed with tears running down his face, his heart pounding. The more she tries to soothe him, the more agitated he becomes.

A college student walks into her parents' bedroom while they're sleeping and pours a glass of water into her mother's dresser drawer.

A physician takes a telephone call from the emergency room at 3 am, receives information about a complex case, and then gives completely inappropriate instructions for the patient's care.

What all these people have in common is that, in the morning, none of them remembers a thing.

These stories—all true—are examples of parasomnias, which are defined as "unpleasant or undesirable behavioral or experiential phenomena during sleep."

What Is a Parasomnia?

"Anything that goes bump in the night is parasomnia," says Dr. Mark Mahowald, a neurologist at the Minnesota Regional Sleep Disorders Center and a leading researcher in this field of sleep disorders.

Parasomnias include sleepwalking and sleep terrors. Bed-wetting , when there's not an underlying urologic condition, also is considered a parasomnia.

While they can be frightening to observe, most parasomnias are benign and require no treatment beyond some simple safety measures to keep people from injuring themselves during an episode.

Parasomnias are more common in children than in adults because the condition most often occurs during deep sleep, which decreases as we age. "Our sleep matures," says Dr. Dainis Irbe, medical director of Pacific Northwest Sleep Association.

What's the Difference Between REM and Non-REM Disorders?

Parasomnias fall into two main categories—disorders of REM sleep and non-REM sleep disorders.

REM, short for "rapid eye movement," sleep is the most active stage of sleep during the second half of the night. This is when most dreams and nightmares occur.

Because we spend more time in REM sleep during the latter part of the night, there is "more opportunity to get those symptoms, usually associated with waking up after a bad dream," says Dr. Irbe. "[The person] might scream, look around, be confused. You can communicate with him, he'll respond, he'll remember what he dreamt about and can tell you in detail."

Normally, REM sleep is accompanied by muscle paralysis, which may be the body's way of protecting itself (and others) during dreams. "Our brains are going into high gear during REM sleep," Dr. Mahowald explains. "[Without the paralysis] we could act on brain activity." People with REM sleep behavior disorder, who are almost always older men, lack that paralysis and physically act out their dreams. "A good example is the man who thinks he's playing football and thinks he's making a catch and injures himself by falling on the floor," says Dr. Mahowald.

Non-REM sleep includes the deep sleep that normally occurs during the first phase of sleep. That's when sleepwalking, confusional arousals, and sleep terrors occur.

Should You Wake a Sleepwalker?

"Sleepwalking," Dr. Mahowald says, "is part of the human condition. Almost every parent of a young child has found the child sleeping somewhere he's not supposed to be." Up to 4% of adults walk in their sleep, and there's evidence that it can be hereditary.

There's some wisdom to the folk advice not to wake a sleepwalker, or a person with sleep terrors, for that matter. Rochelle Zak, MD, at the Sleep-Wake Disorders Center, New York Presbyterian Hospital-Cornell, explains that during these times, people aren't rational and could lash out. "You don't know what to expect," she says. "It's not necessarily that they will cause violence, [but] they're just not fully conscious. What you try to do is help them back to bed." Plus, make sure windows are latched and doors are locked. A gate across the stairs could be helpful, too.

What Are Sleep Terrors?

Sleep terrors, which can occur at night or during daytime naps, are the most extreme form of disorders of arousal. According to Dr. Mahowald, a person may sit or jump up and there is often what family members describe as a blood-curdling scream. The person may even run around or throw things. He appears to be awake, but clearly is not awake and is very difficult to arouse. He may be breathing very rapidly, have prominent sweating, and look absolutely terrified. "Yet if [he's] not awakened during the episode, [he's] totally unaware [of it] in the morning. That's generally true for sleepwalking too. There's almost total amnesia," says Dr. Mahowald.

Another major difference between the nightmares of REM sleep and the sleep terrors of deep sleep is that nightmares involve a complex plot that can be recalled in detail, while the images involved with night terrors are very primitive and simplistic, such as fire, a monster, or the ceiling falling in.

Why Does Bed-wetting Occur?

Bed-wetting, also called enuresis, in people up to age five is not a major concern, Dr. Irbe says. But after that, it's considered a problem, since fewer than 5% of those cases are related to a urinary tract problem. "It could be because of training problems or it could be family problems," he says. "Also, many times, enuresis is associated with sleep deprivation, restless sleep, sleep fragmentation, and sleep apnea ."

Generally, children grow out of parasomnias, and they require no treatment beyond a physician reassuring their parents that the condition is not serious.

How Do You Treat Parasomnias?

If someone's behavior associated with parasomnias are violent, causing injuries to the patient or others, treatment with a class of medications called benzodiazepines can be very effective. However, most doctors consider medication a last resort. "The question is, do you want to give a medicine every single night that we know affects the brain?" Dr. Zak says. "We don't know what effects it has. We don't want to give a child a psychoactive drug every night for something that occurs rarely. Part of [the decision] is how frequently it occurs."

Dr. Mahowald teaches patients to use hypnosis or self-relaxation techniques before they go to sleep. "It appears the arousal still happens, but not the behaviors," he says. "It's quite effective in children and adults, and that's the treatment we'd prefer."

What Are Some Prevention Tips?

Here are some tips for preventing parasomnias:

  • Keep the same sleep schedule and get enough sleep. This will prevent the increase in deep sleep that can trigger sleepwalking, sleep terrors, and other parasomnias.
  • Parents can keep a diary for a week or two of a child's parasomnias, which will usually occur about the same time. Once that time is established, wake the child up about 30 minutes before an event, just enough so the child opens his eyes and recognizes you. Then let him go back to sleep.

Are There Safety Measures?

There are some general safety precautions you can take if you or someone you know experiences parasomnias:

  • Lower the bed to the floor. It's harder to get up out of a mattress on the floor, compared to at the usual height.
  • Sleep in a sleeping bag. It's harder to get out of than typical blankets.
  • If bedrooms are on the second floor, move the bed to the first floor.
  • Latch windows and lock doors.
  • Put gates across stairwells.
  • Put bells or alarms on door knobs.
  • If a person is staying in bed during a sleep terror, he won't hurt himself. Don't try to restrain him; it can make him more agitated.