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Sleep Disorders

The International Classification of Sleep Disorders, third edition (ICSD-3) is the guide for classifying sleep disorders used by most sleep clinic professionals. Published by the American Academy of Sleep Medicine, it includes six cate­gories of disorders:

  1. insomnia (see Lack of Sleep page)
  2. central disorders of hypersomnolence (too much sleepiness)
  3. sleep-related breathing disorders (sleep apneas and related disorders)
  4. circadian rhythm sleep-wake disorders (problems due to shift changes or inability adopt normal day/night patterns)
  5. parasomnias (nightmares and other difficulties that occur during sleep)
  6. sleep-related movement disorders (restless legs syndrome and REM sleep disorder)

There is also an seventh category, "Other sleep disorder." A physician can use that if a case does not fit into any of the other categories.


Hypersomnolence is too much sleepi­ness. The most dangerous disorder in this category is narcolepsy. Narcolepsy is a tendency to fall asleep very suddenly in the middle of ordinary waking activ­ities. The distinguishing characteristic of narcolepsy is inappropriateness of sleep occurrence.

For example, it is dangerous to fall asleep while riding a bicycle, lecturing to a class of students, or driving a car. Normal people may experience intense sleepiness after a heavy meal or sleep deprivation, but narcoleptics fall asleep when most people would stay awake. Ernest Hilgard of Stanford used to say, "Falling asleep at a lecture is normal; falling asleep while you lecture is narcolepsy."

What is narcolepsy? Why is it dangerous?

People with narcolepsy go directly into a state resembling REM sleep. Sleep Onset REM Periods are called SOREMPs, and part of the diagnostic procedures for narco­lepsy is looking for SOREMPs.

What are SOREMPs?

Narcolepsy comes in several varieties, distinguished by whether or not they include cataplexy, which is the relaxation of muscles below the neck, typical of REM sleep. Narcolepsy with cataplexy results in a person collapsing with little warning, going into REM sleep.

Obviously this is a serious problem if a person is performing an activity such as driving a car or swimming. Therefore narcolepsy is considered a serious medical disorder.

The most typical symptoms of narcolepsy are sleep attacks that can last from 30 seconds to 20 minutes but usually last 2-5 minutes. During this time the person has an irresistible urge to sleep.

Some narcoleptics experience micro­sleeps which are tiny episodes of sleep of which the person is unaware. Others experience periods of automatic beha­vior (with amnesia or loss of memory) during the day.

Cataplexy is "an abrupt loss of muscle tone, most often triggered by sudden, strong emotions." It can occur while a person is awake, in which case it is not a sleep disorder. It can also be paired with narcolepsy as part of a sudden-onset REM period. It probably involves the same mechanism which produces muscle paralysis in REM sleep.

One research team (Siegal, Nienhius, Fahringer, Paul, Shriomani, Dement, Mignot, & Chiu, 1991) studied a dog that suffered bouts of cataplexy. The researchers found neurons in the medulla, a midbrain structure, which fired nerve impulses during two conditions: (1) during cataplexy, and (2) during muscle paralysis associated with REM sleep. They suggested, "Cataplexy results from a triggering in waking of the neurons responsible for the suppression of muscle tone in REM sleep."

A person can live a normal and produc­tive life with cataplexy, especially if it is not accompanied by narcolepsy. Theodore Hesburgh served as president of Notre Dame University for 35 years (1952-1987), the longest tenure in that position to date. He suffered from cataplexy, with periodic uncontrolled collapses. However, he was an effective leader and he lived to the age of 97.

Sleep Paralysis

About 30% of normal people find that occasionally, while awakening, they cannot move. This phenom­enon is called sleep paralysis.

Probably a neural center in a midbrain structure called the medulla (the same area that triggers cataplexy) causes sleep paralysis. The muscle inhibition of REM sleep "hangs on" a little too long. The person wakes up paralyzed, unable to move.

What is sleep paralysis?

A student reports a typical episode:

One morning as I was awakening I found myself in this strange state. It was a feeling hard to describe yet it is still clear in my mind.

I could hear my mother in the kitchen; she was talking to my sister as she fried some bacon. Strangely enough I could smell the bacon and could even hear them talking, yet my body was paralyzed.

I wanted to move desperately. I tried yelling out to them to come and help me but my mouth just wouldn't move. I even tried rolling out of bed but could not move a muscle.

My mind began to wander as I lay there helplessly. I soon recalled hearing my mother say something about a state of sleep when breath­ing becomes difficult and you can't move. She always called it a witch riding your back.

I soon snapped out of it and awoke in a rush. I was so glad to have my body under control again. [Author's files]

Another student reported that paralysis-upon-awakening ran in her family on the female side. Her mother and grand­mother both experienced it frequently.

They said the best thing to do was stay calm, go back to sleep, and wake up again. The student practiced this advice, and found that it worked, but said it was still an unpleasant experience.

What response to sleep paralysis was suggested to a student?

Sleep paralysis could be cate­gorized as a hypnopompic state. It takes place during the transition between sleep and wakefulness. Like other hypno­pompic states, it can be accompanied by vivid hallucinations.

How might sleep paralysis be linked to claims of alien abductions?

Some scholars believe that reports of alien abductions are stimulated by episodes of sleep paralysis. Both are marked by inability to move and story-like hallucinations similar to REM dreams (Kristoff, 1999).


Hypersomnia is chronic daytime sleepi­ness, despite the fact that a person is getting enough hours of sleep. Notice the difference between hypersomnia (a sleep disorder) and hypersomnolence (a category of sleep disorders including narcolepsy).

Normal people are disoriented for a moment or two when awakened from deep sleep, but people suffering from hypersomnia can experience something called sleep drunkenness (Roth, Nevsi­malova, and Rechtschaffen, 1972).

Many patients have what's called "sleep drunkenness," in which they are in an alternate stage of consciousness for up to 4 hours upon awakening. These patients are not quite awake and are in and out of stage 1 sleep. Patients can be irritable or violent, fall back to sleep repeatedly, walk into walls, slur their words, and generally act inebriated. Sleep drunkenness can happen when waking up from a nap as well. (Oelke, 2015)

The whole syndrome is called HSD: hypersomnia with sleep drunkenness.

What is HSD, and what are typical experiences of an HSD sufferer?

People with HSD often do not react to an alarm clock, or they awaken just long enough to shut it off. Usually family members or roommates must be enlisted to awaken the person.

After stumbling out of bed, a person with HSD may be confused and disoriented and will return to sleep if left alone. Later the person may not remember having been awakened. Even after a cold shower, a person with HSD may resemble a drunken person.

People with HSD report very deep sleep like anesthesia. Most do not remember any dreams, and they fall asleep within seconds of hitting the bed. They may also have attacks of severe sleepiness during the day, although they can make it to a bed or table, unlike narcoleptics. In other words, there is no sudden cataplexy with hypersomnia.

How does an anti-hypersomnia drug work?

Several drug treatments for hypersomnia exist. Sleepiness is correlated with the transmitter GABA flowing into brain regions after norepinephrine levels (typical of wakefulness) drop. A GABA-antagonist, Flumanzenil, is often effective with people who suffer from hypersomnia.

Somnomania is a term coined by Canadian psychiatrist Alexander Bonkalo. It describes a rare sleep disorder in which a person flies into a violent rage or lashes out violently when awakened.

Casady (1976) gives an example:

Late one night in the year 1600, a German knight, J. von Gut­lingen, was aroused from a deep slumber by his friend and companion-at-arms.

History fails to note the reason for the intrusion on the knight's sleep, but it does record his bizarre response. He leaped out of bed, grabbed a knife, and plunged it into his friend's heart. The German court convicted Gutlingen of murder and condemned him to death. (p.79)

What is somnomania?

Somnomania is distinctive because it occurs mostly in males and usually only during a sudden awakening. Perhaps in homo sapiens this is an evolutionary adaptation to the possibility of being attacked at night while asleep.

REM Behavior Disorder

One of the ICSD diagnostic categories is sleep-related movement disorders. One is known as restless legs syndrome, characterized by itching or burning legs or an irresistible urge to move the legs. Sometimes this will compel a person to walk around to alleviate feelings of restlessness, making sleep difficult.

The other, more dangerous sleep-related movement disorder is REM sleep disorder. This occurs when the muscle-relaxation mechanism in the midbrain fails, leading a person to act out a dream physically while still asleep, eyes closed.

What is REM behavior disorder?

Dr. Carlos Schenck of the Minnesota Regional Sleep Disorder Center in Minneapolis studied many people with this disorder. Most of them were males, middle-aged or older. Blakeslee (1988) wrote:

Schenck's first patient was Donald Dorff, a retired grocer from Minneapolis who gashed his forehead on a bedroom dresser while "dreaming that he was a football star in pads and a uniform, charging an opponent."

After investigating this and many similar cases, Schenck found that 85 percent of people with REM sleep disorder had injured them­selves. Some jumped out of windows while dreaming that their houses were on fire or that someone was trying to kill them.

Others fell off ladders that they climbed in their sleep, or waded into lakes, or drove cars at high speed, or simply fell while roaming around darkened houses. Over half had at some point injured their bed partners, sometimes seriously (Blakeslee, 1988).

Schenck found that most violent sleepers benefited from small doses of anti-convulsant medications. He blames sleep violence on "dysfunctions in areas of the brain responsible for inhibiting motion during sleep."

What is Schenck's explanation of "violent sleep behavior" ?

Schenck's description is strongly reminiscent of Jouvet's cats. Jouvet removed an area near the locus coeruleus (a nucleus in the pons, tucked between the brainstem and the cerebellum).

The cat would sleep until its first REM period. Then it would jump up, with eyes still closed, and run around the cage making attack motions. Jouvet speculated that the cats were acting out their dreams, but one cannot ask a cat about its dreams.

Schenck's findings make Jouvet's speculation plausible. Humans with REM behavior disorder remember their dreams, because part of the syndrome is that people wake up from it fully alert. They testify that they were indeed acting out their dreams.

So Jouvet probably gave us a window into the REM dreams of cats. If so, his cats were dreaming about hunting or fighting, which is not hard to believe. It is said "cats only have one game" which is hunting.

Sleep Apneas and Snoring

Periods of breathlessness are called apneas. Some people have apneic episodes during sleep. These are periods of time up to several seconds during which they do not breathe.

To have a few of these is normal. To have so many that sleep is dis­rupted is not normal. It may cause other problems such as daytime sleepiness.

What are sleep apneas, and how can they trouble a sleeper?

Dement described one person who suffered apnea-related insomnia for 30 years before being tested in a sleep laboratory.

We could not contain our astonish­ment when we found that the patient breathed only when he was awake. Watching the chart paper unfold, we stared open-mouthed as the patient fell asleep and stopped breathing for nearly 100 seconds.

Then, huge scribbles were inked on the respiration chart as he awoke to take gasping breaths into his air-starved lungs. This patient was unable to breathe and sleep at the same time. He had to wake up hundreds of times in order to get enough oxygen to survive the night. (in Block, 1985, p.47)

Over 90% of adult sleep apnea patients are males, usually middle-aged and overweight. Loud snoring or gasping is a universal symptom of the disorder.

Alcohol can worsen the condition. Sleep apnea is more common in people who have large necks, with a collar size over 15 inches.

The two most reliable treatments for chronic obstructive sleep apnea are (1) CPAP machines (Constant Positive Airway Pressure machines), which require sleeping with an air pressure mask strapped to the face, or (2) surgery to remove and tighten tissues at the back of the throat, which eliminates the problem in about 50% of cases.

What are the most reliable treatments for obstructive sleep apneas and snoring?

Chronic, loud snoring is associated with obstructive sleep apnea, a relaxation of throat tissues that blocks the air passages. A cut-off of oxygen results in abnormal acceleration of the heart rate that (doctors long assumed) could trigger a heart attack in some individuals.

That may be an incorrect assumption, however. A study released in 2016 showed no reduction in deaths from cardiac events over a period of years, in patients using CPAP machines to treat sleep apnea.

There were other positive benefits. The CPAP machines reduced levels of snoring and daytime sleepiness and resulted in improved mood, according to the researchers.


Nightmares come in several varieties that are quite distinct. Version 2.13 of the ICSD defined nightmares this way:

Nightmares are frightening dreams that usually awaken the sleeper from REM sleep.

The nightmare is almost always a long, complicated dream that becomes increasingly frightening toward the end. The long, dreamlike feature is essential in making the clinical differentiation from sleep terrors. The awakening occurs out of REM sleep...

The element of fright or anxiety is an essential part of the nightmares. The frightening quality is left to the patient to judge, as some patients are frightened by content that does not appear disturbing to others. (p.163)

Nightmares are distinguished from night terrors, which are less common.

Talking, screaming, striking out, or walking during the nightmare rarely occurs and differentiates nightmare from sleep terrors and REM sleep behavior disorder.

Researchers also distinguish between nightmares and bad dreams. Night­mares wake you up, while bad dreams are simply unpleasant dreams that are recalled after awakening.

What distinction did the ICSD make between nightmares and bad dreams, and how could this affect research?

These operational definitions can affect research, because not everybody uses the International Classification of Sleep Disorders (ICSD) definitions. Robert and Zadra (2014) found that few early researchers used the ICSD definition (where only a bad dream that wakes you up is a nightmare).

They pointed out that "nightmares have been conceptualized as frightening dreams for more than 40 years" without the added provision that nightmares cause awakening. That has an impact on survey numbers, because bad dreams are more common than nightmares that wake people up.

In Robert and Zadra's research, 572 people kept dream diaries for 2-5 weeks. A total of 9,796 dream reports were collected, including 253 nightmares and 431 bad dreams reported by 331 participants.

This meant only 60% of participants had nightmares or bad dreams over the time span of data collection. There were systematic differences between night­mares and bad dreams, however, supporting the ICSD decision to distinguish between them.

The researchers reported:

Physical aggression was the most frequently reported theme in nightmares, whereas interpersonal conflicts predominated in bad dreams. Nightmares were rated by participants as being substantially more emotionally intense than were bad dreams.

...When compared to bad dreams, nightmares were more bizarre and contained substantially more aggressions, failures, and unfortunate endings.

Night Terrors

Night Terrors are most common in chil­dren. Doctors sometimes refer to night terrors by their Latin name pavor nocturnus. Night terrors are character­ized by difficulty breathing, hallucinations, feelings of paralysis, screams, and panic-stricken sleepwalking.

Parents of a child who has night terrors are shocked to find that they cannot awaken or comfort a child who is writhing on the floor screaming. Some children have an attack every night around the same time (at 1 a.m., for example).

After a night terror, the child resumes normal sleep without ever awakening. The child does not remember the attack in the morning and seems unharmed by the experience.

Night terrors do, however, have an impact on concerned parents. They may find it difficult to believe nothing harmful is going on.

The pattern can continue for a period of months, then the attacks stop for no apparent reason. Children just grow out of it.

What are night terrors, and why are they alarming to parents?

Here is how one set of researchers described night terrors:

In pavor nocturnus, the child usually sits up in bed, screams, yells out or moans, continues crying, and speaks unintelligibly. Eyes may be open and there is evidence of increased sympathetic activity including rapid, deep respirations, increased heart rate and blood pressure, and marked perspiration.

The child thrashes about and appears terrified, upset, and/or in pain; nevertheless, he remains inconsolable. This lasts from several minutes to one-half hour after which the child calms rapidly and falls asleep. Trying to hold or restrain the child may actually intensify the outbursts.

...Parents should be reassured that night terrors are well known, common phenomena and usually represent no serious organic or psychological disturbance. (Ferber and Rivinus, 1979, in Webb, 1981, p.47)

Night terrors tend to occur in non-REM sleep, which is why children can thrash around. Another type of non-REM nightmare is the suffocation nightmare, which may be accompanied by a dream of choking, drowning, or having something heavy placed on the chest. It is triggered by sleep apneas, the periods of breathlessness during sleep discussed above.

Far more common than either night terrors or apnea nightmares are so-called anxiety nightmares, classified by ICSD as bad dreams. These are dreams that are unpleasant due to their emotionally unpleasant content. They tend to occur during REM sleep, so they are sometimes called an REM nightmares.

Certain types of bad dreams are very common. At least ten people wrote to my web site over a period of years asking about dreams in which teeth crumble or fall out. That is simply a common nightmare for humans. Perhaps we all remember the sensations of losing a tooth from early childhood.

Other common anxiety nightmares include tornadoes (in North America) or monsoon storms (in Southeast Asia). Other common themes appeared on the list of dream themes (including many held in common by college students and Solomon Islanders) reviewed on the page about dreams. They included being attacked or chased by wild beasts, or being unable to perform a simple activity such as running away from danger.


Blakeslee, S. (1988, Jul 7). Sleepers who are prone to violence benefit from new clinics and drugs. New York Times, p.Y21.

Block, A. J. (1985, May). Sleep apnea and related disorders. Disease of the Month, 31, 1-57.

Casady, M. (1976, January). The sleepy murderers. Psychology Today, pp.79-80.

Kristof, N. D. (1999, July 6) Alien abduction? Science calls it sleep paralysis. New York Times, p. F1.

Oelke, K. (2015, June 28) Clarifying hypersomnia disorders. Sleep Review. Retrieved from:

Roth, B., Nevsimalova, S., & Rechtschaffen, A. (1972) Hypersomnia with "sleep drunkenness." Archives of General Psychiatray, 26, 456-462.

Siegel, J. M., Nienhius, R., Fahringer, H. M., Paul, R., Shiromani, P., Dement, W. C. Mignot, E., & Chiu, C. (1991). Neuronal activity in narcolepsy: Identification of cataplexy-related cells in the medial medulla. Science, 252, 1315-1318.

Zucconi, M. & Ferri, R. (2014) Assessment of sleep disorders and diagnostic procedures. European Sleep Research Society. Retrieved from:

Write to Dr. Dewey at

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