Sleep Disorders Overview

Updated: April 3, 2020 By Ethan Green

There are more than 80 different sleep disorders, though the exact number differs according to which medical classification system is used.

Most sleep specialists and doctors use one of two major systems to diagnose a specific sleep disorder:

  • The Diagnostic and Statistical Manual of Mental Disorders (DSM)
  • The International Classification of Sleep Disorders (ICSD)

The International Classification of Sleep Disorders (ICSD) is the primary diagnostic manual for most sleep researchers and doctors worldwide.

It’s a combined effort from the American Academy of Sleep Medicine and the European, Japanese and Latin American sleep research societies.

The most recent edition of the manual, the ICSD-3, was published in 2014. One of the most notable change was the decision to group the sleep disorders into six main categories instead of four.

There is also technically a seventh category named ‘other sleep disorders’. This allows clinicians to give a code/diagnosis in cases where none of the other sleep disorders explain a patient’s situation.

Below, you’ll find a brief overview of the sleep disorders that either I have personally experienced, or that readers of this website frequently ask me about. Please note that it’s not a complete list of all the possible sleep disorders.

I’ve included links to medical and support organizations where appropriate. And there are my own articles for the various sleep disorders I’ve personally experienced.

1. Insomnia

In the ICSD-3, the definitions of insomnia underwent some major changes. For example, the long-standing concept of primary and secondary insomnia was changed.

Insomnia is defined in the manual as:

…a persistent difficulty with sleep initiation, duration, consolidation, or quality that occurs despite adequate opportunity and circumstances for sleep, and results in some form of daytime impairment

On this site

man snoring in bed


Snoring is a very common problem, with an estimated 40-45% of adults snoring. And many more may be affected by the snoring of their partner or family members.

It doesn’t necessarily mean that you have a sleep disorder just because you snore though. The extent to which it affects your breathing and quality of sleep determines how serious the problem is.

Sleep Apnea

man with apnea wearing a cpap machine

Sleep apnea is a sleep disorder involving pauses when breathing, or breathing shallowly. The pauses, known as apneas, can last for between a few seconds and minutes. Often a person will resume breathing again with a noise like a snore, choke or gasp.

Many people are unaware they suffer from sleep apnea. It’s often someone else, such as a partner, who first notices the problem.

People with sleep apnea often experience poor quality sleep because of it. They also often become accustomed to the ongoing excessive daytime tiredness which accompanies it.

There are three main types of sleep apnea – obstructive sleep apnea, central sleep apnea and mixed sleep apnea/complex sleep apnea syndrome. And there are also various subtypes of sleep apnea.

Catathrenia (nocturnal groaning)

People with catathrenia will sometimes emit a loud noise when exhaling in their sleep. This isn’t to be confused with other disorders such as snoring or apnea.

It doesn’t tend to wake the person up, though anyone else sleeping nearby might be disturbed. In some cases, the noise can sound sexual, which can be embarrassing for the person making the noise and upsetting for a partner to hear.

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3. Central Disorders of Hypersomnolence


Hypersomnia is characterized by excessive sleepiness and daytime sleepiness, as well as difficulty in waking up in the morning even after a good long sleep.

Sufferers of hypersomnia may experience confusional arousals, also known as ‘sleep drunkenness’ (see below). This means they will feel very disorientated upon waking up.


Narcolepsy is the best-known sleep disorder of this type. It’s caused by a defect in a part of the brain. The result is excessive daytime sleepiness, and actually falling asleep during the daytime.

These episodes of falling asleep often occur at very unwanted moments, such as in the middle of a conversation.

People who have narcolepsy may also experience sudden muscle relaxation or collapse (cataplexy). Sometimes this is preceded by emotional reactions like laughter or fear.

Other symptoms include sleep paralysis and hypnagogic hallucinations.

kleine-Levin syndrome

Kleine-Levin syndrome is a rare sleep disorder. It involves a person having periods when they are asleep most of the day and night.

Episodes can last for days, weeks or even longer. In between these periods are usually times when they are completely normal.

Someone with this sleep disorder will wake up for short moments during sleepy periods to use the toilet or eat.

Their behavior during these waking moment is often quite unusual though. They may be disorientated or eat excessively for example. And they may show lacks of inhibition – sometimes sexually in men.

Excessive daytime sleepiness (EDS)

Excessive daytime sleepiness is also perhaps best seen as a symptom rather than a sleep disorder. It isn’t the same as feeling tired because of a bad night’s sleep.

Sufferers are often seen as being lazy, bored or not making an effort, and they rarely seek medical help for this. It can have serious effects on a person’s day-to-day life and functioning though.

Excessive daytime sleepiness usually involves one or more of the following:

  • Feeling tired and lacking energy
  • Falling asleep during the day
  • Needing to sleep a lot at night and struggling to get up
  • Feeling the need to nap frequently during the day

4. Circadian Rhythm Sleep-Wake Disorders

Circadian rhythm disorders are a type of sleep disorder that involves disruption to your internal body clock.

These types are often confused with insomnia, so it’s important to understand the distinction between them and insomnia.

The disorders below can be treated by either gradually retraining your sleep time, with melatonin supplements or light therapy.

Delayed Sleep Phase Syndrome (DSPS)

Delayed Sleep Phase Syndrome often develops at a young age, such as in the teenage years. Someone with DSPS usually goes to sleep later and wakes up later.

They end up being out of sync with the normal hours of other people, or with the rhythm they actually want.

It may be seen by some people as normal teenager behavior. But a problem arises when someone can’t fall asleep and wake up when they would need to.

Their quality of sleep might be fine though – just the timings are out. This out of sync pattern can also develop due to shift work or jet lag.

Advanced Sleep Phase Syndrome (ASPS)

Advanced Sleep Phase Syndrome can be seen as the opposite of Delayed Sleep Phase Syndrome. It’s when a person falls asleep early and wakes up early.

It’s also more common in older people, who may find it very hard to stay awake in the evening, but wake up very early in the morning.

Jet Lag

woman sleeping in an airport

When you travel across time zones, you can become out of sync with the natural cycle of daylight.

This can result in you not being able to sleep at the local time, as well as struggling to wake up at the time you would want to.

Jet Lag can take several days to overcome, but there are steps that can be taken before, during and after traveling to reduce the impact.

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5. Parasomnias

Parasomnias involve disturbed behavior and unusual experiences. They can occur while falling asleep, during sleep, or upon waking.

They often occur during childhood, but can sometimes continue into or start in the adult years.

Some of the following are known as arousal disorders and are the most common forms of parasomnia. For example, sleepwalking, sleep terrors and confusional arousals.

They are when someone partially arouses from deeper sleep. It then appears that they are both asleep and awake due to their behavior.


Sleepwalking (also known as Somnambulism) can result in a wide range of behavior. Some people may get up and calmly carry out simple tasks.

Others may behave in strange ways, and in rare cases with aggressive or destructive behavior. Some people find they do more complex, and potentially dangerous, activities, such as driving.

So although uncommon, it is possible to cause harm to yourself or others when sleepwalking.

Confusional arousals

Confusional arousals are when a person wakes up in the night in a state of disorientation or confusion. It’s usually a mild event and so they fall asleep again easily.

It’s most common in children, though does occur in adults also. There isn’t usually the same complex behavior seen as with sleepwalking, but the person may still sit up or do basic tasks like turn a lamp on, and even stumble around the bedroom.

This is why the disorder is sometimes called sleep drunkenness. In some extreme cases, they may behave in a way that’s dangerous to themselves or others.

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Sleep Terrors

Sleep terrors, sometimes called night terrors, occur during the non-rapid eye movement sleep stages. They can be upsetting to observe because the person, usually a child, is in such a high state of agitation or fear.

They will not normally remember anything that happened during an episode if they wake up. And they will usually calm down naturally while still asleep.


woman awake after nightmare

Nightmares occur during the rapid eye movement (REM) stage of sleep. They will usually wake a person up, often with a vivid memory of a frightening or distressing dream.

The person is usually very alert on waking, with the ability to recall the dream clearly. They may need calming down to fall asleep again.

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Sleep talking

Sleep talking, or somniloquy, involves talking during your sleep without being aware of it. It can range from conversational content to mumbling or nonsense. Usually, no treatment is required unless it becomes a persistent problem.

REM Sleep Behavior Disorder (RBD)

Rapid eye movement behavior disorder involves a person acting out their dreams in their sleep.

A person with RBD does not experience the muscle paralysis that comes with the REM stage of sleep. They are therefore able to move their limbs, talk or act out actions in their dreams.

This can be problematic because of the risk of causing an injury while enacting a dream.


Bedwetting  (or nocturnal enuresis) usually occurs during childhood. It occurs either because they haven’t yet learned bladder control, or they have lost bladder control at some point.

If it begins in adulthood, it’s caused by another medical condition or sleep disorder.

Sleep Paralysis

Many people will experience sleep paralysis at least once in their lifetime. It involves the sensation of not being able to move or talk, either when falling asleep or waking up.

It’s usually accompanied by hallucinations – such as of a demon or other presence often interpreted as scary or evil. And some people may have an out-of-body experience. It can be extremely disturbing to experience even though it’s harmless.

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Exploding Head Syndrome

Exploding head syndrome doesn’t involve any physical pain or damage, despite the scary name. The sufferer will experience a very loud noise inside their head. It might seem like a gunshot, bomb, shouting, or any other loud sound.

It can be quite disturbing and upsetting for the person, and there is no treatment at the moment. Though it is associated with stress and tiredness, so reducing those factors can help.

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Periodic limb movement disorder (PLMD)

restless legs

Periodic limb movement disorder is when a person moves, jerks or flails their limbs during sleep. It’s usually the legs which move, but sometimes the arms also.

This may not wake them up, but it can disrupt their quality of sleep – resulting in daytime sleepiness. Often it’s a partner who is more aware of the problem.

This should also not be confused with the normal movements that many people make while falling asleep.

For example the hypnic jerk – when you feel a jolting movement when dropping off to sleep. Periodic Limb movement disorder can be similar, but continue through the night.

Restless Legs Syndrome (RLS)

Restless legs syndrome is a sleep disorder which can occur during the daytime while a person is awake.

However, the symptoms are usually worse in the evening and at night. This can make it hard for someone to fall asleep and stay asleep.

It’s characterized by an often irresistible urge to move the legs (or arms sometimes). This is often accompanied by intense feelings of discomfort – tingling, burning, itching, cramping or even skin crawling sensations.

Many people find they can relieve the symptoms by moving, exercising, massaging or bathing their legs.

Bruxism – teeth grinding

Bruxism affects around 8% of people and is characterized by the clenching or grinding of teeth throughout the night.

It can result in people needing dental work, having headaches, jaw and facial pain. It can lead to them disturbing their own sleep, and their partner’s, due to the noise.

It’s common with people suffering from apnea, coffee and alcohol drinkers, and smokers. It may also be associated with stress and anxiety.

Understanding the different types of sleep disorders

It can be confusing when researching sleep disorders on the internet. In part, it’s because different websites may be working from different classification systems – or not at all.

This means that you may find one website gives a different description of a sleep disorder to another one. Or that the names suddenly change from one place to the next.

You may also find that one source puts a particular disorder under one category, but another source puts it under a completely different category.

If you’re concerned about your sleep problems, it’s important not to rely on self-diagnosis, and to speak to a medical professional about it. They can provide a diagnosis, guidance and treatment plan.