Sleep disorders are a group of syndromes characterized by disturbance in a person's amount of sleep, quality or timing of sleep, or in behavior while sleeping. There are about 70 different sleep disorders.
Although sleep is a basic behavior in animals as well as humans, researchersstill don't completely understand it. In the past 30 years, however, researchers have learned about the pattern of different types of sleep and its effects on breathing, heart rate, brain waves, and so on.
There are five stages of human sleep. Four stages occur during "non-rapid eyemovement (NREM) sleep," featuring unique brain wave patterns and body changes. Dreaming occurs in the fifth stage, known as "rapid eye movement (REM)" sleep. Stage 1 NREM sleep begins as a person falls asleep, progressing into Stage 2 NREM sleep, the beginning of "true" sleep. Experts can identify this stage by looking at a person's brain waves on a graph of brain activity. About 50% of sleep time is stage 2 REM sleep. Stages 3 and 4 (also called "delta" or"slow-wave sleep") are the deepest levels of human sleep and take up 10-20%of sleep time. Finally comes Stage 5 -- REM sleep, which accounts for 20-25%of total sleep time. REM sleep, during which a person's eyes move rapidly back and forth behind closed eyelids, usually begins about 90 minutes after theperson falls asleep. It alternates with NREM sleep about every hour and a half throughout the night. REM periods get longer during the night.
Sleep cycles vary with a person's age. Children and adolescents have longer periods of stage 3 and stage 4 NREM sleep than do middle aged or elderly adults. Total REM sleep also declines with age.
The average length of nighttime sleep varies among people. Most people sleepbetween seven and nine hours a night. In temperate climates, however, peopleoften notice that sleep time varies with the seasons. It's not unusual for people in North America and Europe to sleep about 40 minutes longer per night during the winter.
Experts classify sleep disorders based on their cause. Most sleep disorders are "secondary" -- that is, they are caused by other things such as mental disorders, prescription medications, substance abuse, or medical conditions. Sleep disorders that aren't caused by these things are considered to be "primary" disorders.
One of the best-known kinds of sleep disorders is insomnia -- the inability to fall asleep. An occasional problem in falling asleep isn't considered to beinsomnia; for a diagnosis, the person must have problems getting to sleep orstaying asleep for at least one month. It's estimated that 35% of adults inthe United States experience this problem during any given year, but the number of these adults who are experiencing true primary insomnia is unknown. Primary insomnia is usually caused by a traumatic event related to sleep or bedtime. People who experience primary insomnia are often anxious about not beingable to sleep. They may then associate all sleep-related things (their bed,bedtime, and so on) with frustration, making the problem worse. The person then becomes more stressed about not sleeping. Insomnia usually begins when theperson is a young adult or in middle age.
At the opposite end of the sleep disorder spectrum is the person who sleeps too much -- this is called "hypersomnia." The patient either sleeps a long time during the day, or takes quick naps each day with normal sleep at night. Sometimes, patients with hypersomnia have problems waking in the morning and may appear confused or angry. This condition is sometimes called sleep drunkenness and is more common in males. The number of people with hypersomnia is unknown, although 5-10% of patients in sleep disorder clinics have the disorder.Primary hypersomnia usually affects young adults between the ages of 15 and30.
Restless legs syndrome (RLS) can cause either insomnia or hypersomnia in adults. Patients with RLS wake up because of cramps or twitches in their calves,and therefore they feel sleepy the next day. RLS patients have a crawly or aching feeling in their calves that can be relieved by moving or rubbing the legs. RLS often prevents the patient from falling asleep until the early hoursof the morning, when the condition is less intense.
Kleine-Levin syndrome is a recurrent form of sleepiness that affects a personthree or four times a year. Doctors don't know the cause of this syndrome, but it causes two to three days of excess sleeping 18 to 20 hours per day, extremely sexual behavior, compulsive eating, and irritability. Men are three times more likely than women to have the syndrome. There is no cure for this disorder.
Narcolepsy is a sleep problem in which a person has recurrent "sleep attacks"lasting between 10-20 minutes. Upon awakening, the patient feels refreshed but then feels sleepy again several hours later. Narcolepsy has three major symptoms in addition to sleep attacks: a sudden fall due to muscle tone loss, hallucinations, and sleep paralysis. Hallucinations may occur just before falling asleep or right after waking up and are associated with an episode of REMsleep. Sleep paralysis occurs during the transition from being asleep to waking up. About 40% of patients with narcolepsy have or have had another mentaldisorder. Although narcolepsy is often regarded as an adult disorder, it hasbeen reported in children as young as 3 years old.
Breathing-related sleep disorders are syndromes in which the patient's sleepis interrupted by problems with breathing. There are three types of breathing-related sleep disorders:
- Obstructive sleep apnea syndrome is the mostcommon form of breathing-related sleep disorder, marked by episodes of blockage in the upper airway during sleep. It's found primarily in obese people. Patients with this disorder typically alternate between periods of snoring orgasping (when their airway is partly open) and periods of silence (when theirairway is blocked). Very loud snoring is a clue to this disorder.
- Central sleep apnea syndrome mostly occurs in elderly patients with heart or neurological conditions that affect their ability to breathe properly. It isn'tassociated with airway blockage, and it may be related to brain disease.
- Central alveolar hypoventilation syndrome is found most often in extremely obese people. While the patient's airway is clear, the oxygen level in theblood is too low.
- Mixed-type sleep apnea syndrome. This disorder combines symptoms of both the above sleep problems.
Circadian rhythm sleep disorders are caused by a difference between the person's daily sleep/wake patterns and demands of social activities, shift work, or travel. The term "circadian" comes from a Latin word meaning "daily."
There are three circadian rhythm sleep disorders: Delayed sleep phase, jet lag, and shift work type. In a "delayed sleep phase," the sufferer goes to bedand gets up later than most people. Jet lag is caused by travel to a new timezone, temporarily throwing off a person's circadian rhythm. Shift work sleepdisorder does the same thing, but this is more permanent, since the shift inschedule is caused by the person's job. People who are ordinarily early risers appear to be more vulnerable to jet lag and shift work-related circadian rhythm disorders than people who are "night owls."
In some sleep disorders, the patient's behavior is affected by specific sleepstages or transitions between sleeping and waking. Nightmare disorder is oneversion of this, in which the patient is awakened by frightening dreams andis fully alert on awakening. Between 10-50% of children between 3 and 5 havenightmares. The nightmares occur during REM sleep, usually in the second halfof the night. The child is usually able to remember the content of the nightmare and may be afraid to go back to sleep. More females than males have thisdisorder, although some experts suspect it may be that women are more likelyto report the problem. Nightmare disorder is most likely to occur in peopleunder severe or traumatic stress.
Sleep terror (also called "night terrors") is a disorder of childhood in which the youngster seems to wake up screaming or crying, sweating or shaking --but in fact, the child is still asleep. It can be very difficult to awaken achild in this condition, and indeed, many experts recommend allowing the child to remain asleep. Sleep terror disorder affects about 3% of all children, usually between the ages of 4-12 years old; the problem is usually outgrown byadolescence. Fewer than 1% of adults have the disorder. Unlike nightmares, sleep terrors typically occur in stage 3 or stage 4 NREM sleep during the first third of the night. The patient may be confused or disoriented for severalminutes, and not be able to remember the dream itself. Often, the child fallsasleep again and doesn't remember the episode the next morning. In adults, it usually begins between the ages of 20 and 30. In children, more boys than girls have the disorder, but in adulthood the condition affects men and womenequally.
Sleepwalking disorder (or somnambulism) occurs when a person is able to makecomplex movements during sleep, including walking. Like sleep terror disorder, sleepwalking occurs during stage 3 and stage 4 NREM sleep during the firstpart of the night. If the patient is awakened during a sleepwalking episode,he or she may be disoriented and have no memory of the behavior. In additionto walking around, patients with sleepwalking disorder have been reported toeat, use the bathroom, unlock doors, or talk to others. It is estimated that10-30% of children have at least one episode of sleepwalking, but only 1-5% meet the criteria for sleepwalking disorder. The disorder is most common in children 8-12 years old. It is unusual for sleepwalking to occur for the firsttime in adults.
Unlike sleepwalking, REM sleep behavior disorder occurs later in the night and causes the patient to perform often violent physical movements. Unlike night terrors, the patients usually can remember what they were dreaming at the time.
In addition to the primary sleep disorders, there are also three categories of sleep disorders that are linked with other physical or mental disorders.
Many mental disorders, especially depression or one of the anxiety disorders,can cause sleep disturbances. They are the most common cause of chronic insomnia.
Some patients with chronic neurological conditions like Parkinson's disease or Huntington's disease may develop sleep disorders. Sleep disorders also havebeen associated with viral encephalitis, brain disease, and high or low levels of thyroid activity.