The most common sleep disorders include:

- Bruxism, involuntarily grinding or clenching of the teeth while sleeping.

- Catathrenia, nocturnal groaning during prolonged exhalation.

- Delayed sleep phase disorder (DSPD), inability to awaken and fall asleep at socially acceptable times but no problem with sleep maintenance, a disorder of circadian rhythms. Other such disorders are advanced sleep phase disorder (ASPD), non-24-hour sleep–wake disorder (non-24) in the sighted or in the blind, and irregular sleep wake rhythm, all much less common than DSPD, as well as the situational shift work sleep disorder.

- Hypopnea syndrome, abnormally shallow breathing or slow respiratory rate while sleeping.

- Idiopathic hypersomnia, a primary, neurologic cause of long-sleeping, sharing many similarities with narcolepsy.

- Insomnia disorder (primary insomnia), chronic difficulty in falling asleep and/or maintaining sleep when no other cause is found for these symptoms. Insomnia can also be comorbid with or secondary to other disorders.

- Kleine–Levin syndrome, a rare disorder characterized by persistent episodic hypersomnia and cognitive or mood changes.

- Narcolepsy, including excessive daytime sleepiness (EDS), often culminating in falling asleep spontaneously but unwillingly at inappropriate times. About 70% of those who have narcolepsy also have cataplexy, a sudden weakness in the motor muscles that can result in collapse to the floor while retaining full conscious awareness.

- Night terror, "Pavor nocturnus", sleep terror disorder, an abrupt awakening from sleep with behavior consistent with terror.

- Nocturia, a frequent need to get up and urinate at night. It differs from enuresis, or bed-wetting, in which the person does not arouse from sleep, but the bladder nevertheless empties.

- Parasomnias, disruptive sleep-related events involving inappropriate actions during sleep, for example sleep walking, night-terrors and catathrenia.

- Periodic limb movement disorder (PLMD), sudden involuntary movement of arms and/or legs during sleep, for example kicking the legs. Also known as nocturnal myoclonus. See also Hypnic jerk, which is not a disorder.

- Rapid eye movement sleep behavior disorder (RBD), acting out violent or dramatic dreams while in REM sleep, sometimes injuring bed partner or self (REM sleep disorder or RSD).

- Restless legs syndrome (RLS), an irresistible urge to move legs. RLS sufferers often also have PLMD.

- Shift work sleep disorder (SWSD), a situational circadian rhythm sleep disorder. (Jet lag was previously included as a situational circadian rhythm sleep disorder, but it doesn't appear in DSM-5 (see Diagnostic and Statistical Manual of Mental Disorders)).

- Sleep apnea, obstructive sleep apnea, obstruction of the airway during sleep, causing lack of sufficient deep sleep, often accompanied by snoring. Other forms of sleep apnea are less common. When air is blocked from entering into the lungs, the individual unconsciously gasps for air and sleep is disturbed. Stops of breathing of at least ten seconds, 30 times within seven hours of sleep, classifies as apnea. Other forms of sleep apnea include central sleep apnea and sleep-related hypoventilation.

- Sleep paralysis, characterized by temporary paralysis of the body shortly before or after sleep. Sleep paralysis may be accompanied by visual, auditory or tactile hallucinations. Not a disorder unless severe. Often seen as part of narcolepsy.

- Sleepwalking or "somnambulism", engaging in activities normally associated with wakefulness (such as eating or dressing), which may include walking, without the conscious knowledge of the subject.

- Somniphobia, one cause of sleep deprivation, a dread/ fear of falling asleep or going to bed. Signs of the illness include anxiety and panic attacks before and during attempts to sleep.

Nocturnal awakenings are more common in older patients and have been associated with depressive disorders, chronic pain, obstructive sleep apnea, obesity, alcohol consumption, hypertension, gastroesophageal reflux disease, heart disease, menopause, prostate problems, and bipolar disorders.

Nocturnal awakenings can be mistaken as shift work disorder.

The true primary hypersomnias include these: narcolepsy (with and without cataplexy); idiopathic hypersomnia; and recurrent hypersomnias (like Klein-Levin syndrome).

Hypersomnia can be primary (of central/brain origin), or it can be secondary to any of numerous medical conditions. More than one type of hypersomnia can coexist in a single patient. Even in the presence of a known cause of hypersomnia, the contribution of this cause to the complaint of EDS needs to be assessed. When specific treatments of the known condition do not fully suppress EDS, additional causes of hypersomnia should be sought. For example, if a patient with sleep apnea is treated with CPAP (continuous positive airway pressure) which resolves their apneas but not their EDS, it is necessary to seek other causes for the EDS. Obstructive sleep apnea “occurs frequently in narcolepsy and may delay the diagnosis of narcolepsy by several years and interfere with its proper management.”

This sleep disorder frequently applies when patients report not feeling tired despite their subjective perception of not having slept. Generally, they may describe experiencing several years of no sleep, short sleep, or non-restorative sleep. Otherwise, patients appear healthy, both psychiatrically and medically. (That this condition is often asymptomatic could explain why it is relatively unreported.)

However, upon clinical observation, it is found that patients may severely overestimate the time they took to fall asleep—often reporting having slept half the amount of time indicated by polysomnogram or electroencephalography (EEG), which may record normal sleep. Observing such discrepancy between subjective and objective reports, clinicians may conclude that the perception of poor sleep is primarily illusionary.

Alternatively, some people may report excessive daytime sleepiness or chronic disabling sleepiness, while no sleep disorder has been found to exist. Methods of diagnosing sleepiness objectively, such as the Multiple Sleep Latency Test do not confirm the symptom"true" sleepiness is not observed despite the complaint. (It may be speculated that such reports of daytime sleepiness may be a result of the nocebo response —the reverse of the placebo effect—due to patient expectations of adverse effects from their subjective perception of poor sleep.)

Finally, on the opposite end of the spectrum, other patients may report feeling that they have slept much longer than is observed. It has been proposed that this experience be subclassified under sleep state misperception as "positive sleep state misperception", "reverse sleep state misperception", and "negative sleep state misperception".

Middle-of-the-night insomnia (MOTN) is characterized by having difficulty returning to sleep after waking up during the night or very early in the morning. It is also called nocturnal awakenings, middle of the night awakenings, sleep maintenance insomnia, and middle insomnia. This kind of insomnia (sleeplessness) is different from initial or sleep-onset insomnia, which consists of having difficulty falling asleep at the beginning of sleep.

The disrupted sleep patterns caused by middle-of-the-night insomnia make many sufferers of the condition complain of fatigue the following day. Excessive daytime sleepiness is reported nearly two times higher by individuals with nocturnal awakenings than by people who sleep through the night.

Sleep research conducted already in the 1990s showed that such waking up during the night may be a natural sleep pattern, rather than a form of insomnia. If interrupted sleep (called "biphasic sleeping" or "bimodal sleep") is perceived as normal and not referred to as "insomnia", less distress is caused and a return to sleep usually occurs after about one hour.

There are over 30 recognized kinds of dyssomnias. Major groups of dyssomnias include:

- Intrinsic sleep disorders – 12 disorders recognized, including

- idiopathic hypersomnia,

- narcolepsy,

- periodic limb movement disorder,

- restless legs syndrome,

- sleep apnea,

- sleep state misperception.

- Extrinsic sleep disorders – 13 disorders recognized, including

- alcohol-dependent sleep disorder,

- food allergy insomnia,

- inadequate sleep routine.

- Circadian rhythm sleep disorders, both intrinsic and extrinsic – 6 disorders recognized, including

- advanced sleep phase syndrome,

- delayed sleep phase syndrome,

- jetlag,

- shift work sleep disorder.

The patient has a complaint of insomnia while sleep quality and duration are normal. Polysomnographic monitoring demonstrates normal sleep latency, a normal number of arousals and awakenings, and normal sleep duration with or without a multiple sleep latency test that demonstrates a mean sleep latency of greater than 10 minutes. No medical or mental disorder produces the complaint. Other sleep disorders producing insomnia are not present to a degree that would explain the patient’s complaint.

Symptoms of insomnia:

- difficulty falling asleep, including difficulty finding a comfortable sleeping position

- waking during the night and being unable to return to sleep

- feeling unrefreshed upon waking

- daytime sleepiness, irritability or anxiety

Sleep-onset insomnia is difficulty falling asleep at the beginning of the night, often a symptom of anxiety disorders. Delayed sleep phase disorder can be misdiagnosed as insomnia, as sleep onset is delayed to much later than normal while awakening spills over into daylight hours.

It is common for patients who have difficulty falling asleep to also have nocturnal awakenings with difficulty returning to sleep. Two-thirds of these patients wake up in the middle of the night, with more than half having trouble falling back to sleep after a middle-of-the-night awakening.

Early morning awakening is an awakening occurring earlier (more than 30 minutes) than desired with an inability to go back to sleep, and before total sleep time reaches 6.5 hours. Early morning awakening is often a characteristic of depression.

Dyssomnias are a broad classification of sleeping disorders involving difficulty getting to sleep, remaining asleep, or of excessive sleepiness.

Dyssomnias are primary disorders of initiating or maintaining sleep or of excessive sleepiness and are characterized by a disturbance in the amount, quality, or timing of sleep.

Patients may complain of difficulty getting to sleep or staying asleep, intermittent wakefulness during the night, early morning awakening, or combinations of any of these. Transient episodes are usually of little significance. Stress, caffeine, physical discomfort, daytime napping, and early bedtimes are common factors.

Poor sleep quality can occur as a result of, for example, restless legs, sleep apnea or major depression. Poor sleep quality is caused by the individual not reaching stage 3 or delta sleep which has restorative properties.

Major depression leads to alterations in the function of the hypothalamic-pituitary-adrenal axis, causing excessive release of cortisol which can lead to poor sleep quality.

Nocturnal polyuria, excessive nighttime urination, can be very disturbing to sleep.

According to the International Classification of Sleep Disorders, Revised (ICSD-R, 2001), the circadian rhythm sleep disorders share a common underlying chronophysiologic basis:

Incorporating minor updates (ICSD-3, 2014), the diagnostic criteria for delayed sleep phase disorder are:

Some people with the condition adapt their lives to the delayed sleep phase, avoiding morning business hours as much as possible. The ICSD's severity criteria are:

- Mild: Two-hour delay (relative to the desired sleep time) associated with little or mild impairment of social or occupational functioning.

- Moderate: Three-hour delay associated with moderate impairment.

- Severe: Four-hour delay associated with severe impairment.

Some features of DSPD which distinguish it from other sleep disorders are:

- People with DSPD have at least a normal—and often much greater than normal—ability to sleep during the morning, and sometimes in the afternoon as well. In contrast, those with chronic insomnia do not find it much easier to sleep during the morning than at night.

- People with DSPD fall asleep at more or less the same time every night, and sleep comes quite rapidly if the person goes to bed near the time he or she usually falls asleep. Young children with DSPD resist going to bed before they are sleepy, but the bedtime struggles disappear if they are allowed to stay up until the time they usually fall asleep.

- DSPD patients usually sleep well and regularly when they can follow their own sleep schedule, e.g., on weekends and during vacations.

- DSPD is a chronic condition. Symptoms must have been present for at least three months before a diagnosis of DSPD can be made.

Often people with DSPD manage only a few hours sleep per night during the working week, then compensate by sleeping until the afternoon on weekends. Sleeping late on weekends, and/or taking long naps during the day, may give people with DSPD relief from daytime sleepiness but may also perpetuate the late sleep phase.

People with DSPD can be called "night owls". They feel most alert and say they function best and are most creative in the evening and at night. People with DSPD cannot simply force themselves to sleep early. They may toss and turn for hours in bed, and sometimes not sleep at all, before reporting to work or school. Less-extreme and more-flexible night owls are within the normal chronotype spectrum.

By the time those who have DSPD seek medical help, they usually have tried many times to change their sleeping schedule. Failed tactics to sleep at earlier times may include maintaining proper sleep hygiene, relaxation techniques, early bedtimes, hypnosis, alcohol, sleeping pills, dull reading, and home remedies. DSPD patients who have tried using sedatives at night often report that the medication makes them feel tired or relaxed, but that it fails to induce sleep. They often have asked family members to help wake them in the morning, or they have used multiple alarm clocks. As the disorder occurs in childhood and is most common in adolescence, it is often the patient's parents who initiate seeking help, after great difficulty waking their child in time for school.

The current formal name established in the third edition of the International Classification of Sleep Disorders (ICSD-3) is delayed sleep-wake phase disorder. Earlier, and still common, names include delayed sleep phase disorder (DSPD), delayed sleep phase syndrome (DSPS), and circadian rhythm sleep disorder, delayed sleep phase type (DSPT).

The primary symptoms of shift work sleep disorder are insomnia and excessive sleepiness associated with working (and sleeping) at non-standard times. Shift work sleep disorder is also associated with falling asleep at work. Total daily sleep time is usually shortened and sleep quality is less in those who work night shifts compared to those who work day shifts. Sleepiness is manifested as a desire to nap, unintended dozing, impaired mental acuity, irritability, reduced performance, and accident proneness. Shift work is often combined with extended hours of duty, so fatigue can be a compounding factor. The symptoms coincide with the duration of shift work and usually remit with the adoption of a conventional sleep-wake schedule. The boundary between a "normal response" to the rigors of shift work and a diagnosable disorder is not sharp.

A systematic review found that traumatic childhood experiences (such as family conflict or sexual trauma) significantly increases the risk for a number of sleep disorders in adulthood, including sleep apnea, narcolepsy, and insomnia. It is currently unclear whether or not moderate alcohol consumption increases the risk of obstructive sleep apnea.

In addition, an evidence-based synopses suggests that the sleep disorder, idiopathic REM sleep behavior disorder (iRBD), may have a hereditary component to it. A total of 632 participants, half with iRBD and half without, completed self-report questionnaires. The results of the study suggest that people with iRBD are more likely to report having a first-degree relative with the same sleep disorder than people of the same age and sex that do not have the disorder. More research needs to be conducted to gain further information about the hereditary nature of sleep disorders.

A population susceptible to the development of sleep disorders is people who have experienced a traumatic brain injury (TBI). Because many researchers have focused on this issue, a systematic review was conducted to synthesize their findings. According to their results, TBI individuals are most disproportionately at risk for developing narcolepsy, obstructive sleep apnea, excessive daytime sleepiness, and insomnia. The study's complete findings can be found in the table below:

Four of them are intrinsic (from Latin "intrinsecus", on the inside, inwardly), "built-in":

- Advanced sleep phase disorder (ASPD), a.k.a. advanced sleep phase syndrome (ASPS), characterized by difficulty staying awake in the evening and difficulty staying asleep in the morning

- Delayed sleep phase disorder (DSPD), a.k.a. delayed sleep phase syndrome (DSPS), characterized by a much later than normal timing of sleep onset and offset and a period of peak alertness in the middle of the night

- Irregular sleep–wake rhythm, which presents as sleeping at very irregular times, and usually more than twice per day (waking frequently during the night and taking naps during the day) but with total time asleep typical for the person's age

- Non-24-hour sleep–wake disorder (non-24, a.k.a. hypernychthemeral syndrome), in which the affected individual's sleep occurs later and later each day, with the period of peak alertness also continuously moving around the clock from day to day.

Delayed sleep phase disorder (DSPD), more often known as delayed sleep phase syndrome and also as delayed sleep-wake phase disorder, is a chronic dysregulation of a person's circadian rhythm (biological clock), compared to the general population and relative to societal norms. The disorder affects the timing of sleep, peak period of alertness, the core body temperature rhythm, and hormonal and other daily cycles. People with DSPD generally fall asleep some hours after midnight and have difficulty waking up in the morning. People with DSPD probably have a circadian period significantly longer than 24 hours. Depending on the severity, the symptoms can be managed to a greater or lesser degree, but no cure is known, and research suggests a genetic origin for the disorder.

Affected people often report that while they do not get to sleep until the early morning, they do fall asleep around the same time every day. Unless they have another sleep disorder such as sleep apnea in addition to DSPD, patients can sleep well and have a normal need for sleep. However, they find it very difficult to wake up in time for a typical school or work day. If they are allowed to follow their own schedules, e.g. sleeping from 3:00 am to 12:00 noon, their sleep is improved and they may not experience excessive daytime sleepiness. Attempting to force oneself onto daytime society's schedule with DSPD has been compared to constantly living with jet lag; DSPD has, in fact, been referred to as "social jet lag".

Researchers in 2017 linked DSPD to at least one genetic mutation. The syndrome usually develops in early childhood or adolescence. An adolescent version may disappear in late adolescence or early adulthood; otherwise, DSPD is a lifelong condition. Prevalence among adults, equally distributed among women and men, is around 0.15%, or three in 2,000. Prevalence among adolescents is as much as 7–16%.

DSPD was first formally described in 1981 by Elliot D. Weitzman and others at Montefiore Medical Center. It is responsible for 7–10% of patient complaints of chronic insomnia. However, since many doctors are unfamiliar with the condition, it often goes untreated or is treated inappropriately; DSPD is often misdiagnosed as primary insomnia or as a psychiatric condition. DSPD can be treated or helped in some cases by careful daily sleep practices, morning light therapy, evening dark therapy, earlier exercise and meal times, and medications such as melatonin and modafinil; the former is a natural neurohormone partly responsible for the human body clock. At its most severe and inflexible, DSPD is a disability. A chief difficulty of treating DSPD is in maintaining an earlier schedule after it has been established, as the patient's body has a strong tendency to reset the sleeping schedule to its intrinsic late times. People with DSPD may improve their quality of life by choosing careers that allow late sleeping times, rather than forcing themselves to follow a conventional 9-to-5 work schedule.

Insomnia and wake-time sleepiness are related to misalignment between the timing of the non-standard wake–sleep schedule and the endogenous circadian propensity for sleep and wake. In addition to circadian misalignment, attempted sleep at unusual times can be interrupted by noise, social obligations, and other factors. Finally, there is an inevitable degree of sleep deprivation associated with sudden transitions in sleep schedule.

One of these disorders is extrinsic (from Latin "extrinsecus", from without, on the outside) or circumstantial:

- Shift work sleep disorder, which affects people who work nights or rotating shifts.

Formerly, jet lag, too, was classified as an extrinsic type circadian rhythm disorder.

Symptoms of UARS are similar to those of obstructive sleep apnea, but are usually less severe. Fatigue, daytime sleepiness, unrefreshing sleep, and frequent awakenings during sleep are the most common symptoms.

Many patients experience chronic insomnia that creates both a difficulty falling asleep and staying asleep. As a result, patients typically experience frequent sleep disruptions. Loud snoring also serves as a possible indicator of the syndrome, but is not a symptom required for diagnosis.

Some patients experience hypotension, which may cause lightheadedness, and patients with UARS are also more likely to experience headaches and irritable bowel syndrome.

Parasomnia disorders are classified into the following categories:

- arousal disorders

- sleep-wake transition disorders

- parasomnias associated with REM sleep

Symptoms reported by patients forced into a 24-hour schedule are similar to those of sleep deprivation and can include:

- Apraxia including ideational apraxia, ideomotor apraxia, kinetic apraxia, limb apraxia, verbal apraxia

- Cognitive dysfunction

- Difficulties concentrating

- Confusion

- Depressed mood

- Diarrhea

- Extreme nausea

- Extreme fatigue

- Hair loss

- Headaches

- Impaired balance

- Photosensitivity

- Joint pain

- Loss of muscle coordination (ataxia)

- Menstrual irregularities

- Muscle pain

- Suicidal thoughts

- Weight gain

- Hallucinations

Under DSM-5 criteria, there are 11 diagnostic groups that comprise sleep-wake disorders. These include, Insomnia disorder, Hypersomnolence disorder, Narcolepsy, Obstructive sleep apnea hypopnea, Central sleep apnea, Sleep-related hypoventilation, Circadian rhythm sleep-wake disorders, Non–rapid eye movement (NREM) sleep arousal disorders, Nightmare disorder, Rapid eye movement (REM) sleep behavior disorder, Restless legs syndrome, and substance-medication-induced sleep disorder. Sexsomnia is classified under NREM arousal parasomnia.

Non-24-hour sleep–wake disorder (non-24), is one of several chronic circadian rhythm sleep disorders (CRSDs). It is defined as a "chronic steady pattern comprising [...] daily delays in sleep onset and wake times in an individual living in society." Symptoms result when the non-entrained (free-running) endogenous circadian rhythm drifts out of alignment with the light/dark cycle in nature.

The sleep pattern can be quite variable. People with a circadian rhythm that is quite near to 24 hours may be able to sleep on a conventional, socially acceptable schedule, that is, at night. Others, with a "daily" cycle upwards of 25 hours or more may need to adopt a sleep pattern that is congruent with their free-running circadian clock, shifting their sleep times daily, thereby often obtaining satisfactory sleep but suffering social and occupational consequences.

The majority of people with non-24 are totally blind, and the failure of entrainment is explained by an absence of photic input to the circadian clock. These people's brains may have normal "body clocks", but the clocks do not receive input from the eyes about environmental light levels, as that requires a functioning retina, optic nerve and visual processing center.

The disorder also occurs in sighted people for reasons that are not well understood. Their circadian rhythms are not normal, often running to more than 25 hours. Their visual systems may function normally but their brains are incapable of making the large adjustment to a 24-hour schedule.

Though often referred to as non-24, for example by the FDA, the disorder is also known by the following terms:

- Non-24-hour sleep–wake syndrome

- Non-24-hour sleep–wake disorder

- Non-24-hour sleep-wake rhythm disorder

- Free running disorder (FRD)

- Hypernychthemeral disorder

- Circadian rhythm sleep disorder – free-running type

- Circadian rhythm sleep disorder – nonentrained type

- N24HSWD

- Non-24-hour circadian rhythm disorder

The disorder in its extreme form is an invisible disability that can be "extremely debilitating in that it is incompatible with most social and professional obligations".

Upper airway resistance syndrome is caused when the upper airway narrows without closing. Consequently, airflow is either reduced or compensated for through an increase in inspiratory efforts. This increased activity in inspiratory muscles leads to the arousals during sleep which patients may or may not be aware of.

A typical UARS patient is not obese and possesses a triangular face and misaligned jaw, which can result in a smaller amount of space behind the base of the tongue. Patients may have other anatomical abnormalities that can cause UARS such as deviated septum or nasal valve collapse. UARS affects equal numbers of males and females. It is unclear as to whether UARS is merely a phase that occurs between simple snoring and sleep apneas, or whether UARS is a syndrome that describes a deviation from normal upper airway physiology.

Children with UARS may experience symptoms due to minor anomalies of the facial bones or due to enlarged tonsils or adenoids.

Caffeine-induced sleep disorder is a psychiatric disorder that results from overconsumption of the stimulant caffeine. "When caffeine is consumed immediately before bedtime or continuously throughout the day, sleep onset may be delayed, total sleep time reduced, normal stages of sleep altered, and the quality of sleep decreased." Caffeine reduces slow-wave sleep in the early part of the sleep cycle and can reduce rapid eye movement sleep later in the cycle. Caffeine increases episodes of wakefulness, and high doses in the late evening can increase sleep onset latency. In elderly people, there is an association between use of medication containing caffeine and difficulty in falling asleep.

The specific criteria for this disorder in the fourth version of the "Diagnostic and Statistical Manual of Mental Disorders" (DSM-IV) include that there must be a significant inability to sleep which is caused entirely by the physiological effects of caffeine as proven by an examination; if sleeping issues can be accounted for due to a breathing-related sleep disorder, narcolepsy, a circadian rhythm sleep disorder or a mental disorder, then caffeine-induced sleep disorder is not the cause. This condition causes a notable impairment in functioning in sufferers.

Overconsumption:

Excessive ingestion of caffeine can lead to a state of intoxication. This period of intoxication is characterized by restlessness, agitation, excitement, rambling thought or speech, and even insomnia. Even doses of caffeine relating to just one cup of coffee can increase sleep latency and decrease the quality of sleep especially in non-REM deep sleep. A dose of caffeine taken in the morning can have these effects the following night, so one of the main practices of sleep hygiene a person can do is to cease the consumption of caffeine.