Understanding Sleep Disorders

Sleep disorders are conditions that disturb the amount, quality or timing of sleep, or that involve unusual behaviors or experiences during sleep, and that cause distress or problems with daytime functioning. They range from very common conditions such as insomnia and obstructive sleep apnea to rarer ones such as narcolepsy. Sleep disorders are classified in detail in the International Classification of Sleep Disorders (ICSD-3-TR), and the main ones also appear in the DSM-5-TR's chapter on sleep-wake disorders.

Sleep matters for psychology because it is closely tied to mood, memory, attention and emotional regulation. This overview explains how normal sleep works, describes the main groups of sleep disorder, and outlines how they are diagnosed and treated. It is educational; anyone with persistent sleep problems should speak with a doctor.

Sleep Basics and Architecture

Sleep stages

Sleep is not a single state. Since 2007, the American Academy of Sleep Medicine has divided it into non-rapid eye movement (NREM) sleep, with three stages, and rapid eye movement (REM) sleep:

These stages cycle roughly every 90 minutes, with more deep sleep early in the night and longer REM periods toward morning. The proportions shift across the lifespan: infants spend much more time in REM, while older adults get less deep sleep and wake more often.

What regulates sleep

Swiss researcher Alexander Borbély's influential two-process model (1982) proposes that sleep timing results from two interacting processes. Process S is sleep pressure, which builds the longer we are awake (partly through the build-up of a chemical called adenosine, which caffeine blocks). Process C is the circadian rhythm, a roughly 24-hour internal clock in the brain's suprachiasmatic nucleus, set mainly by light and signalled partly through the hormone melatonin. Many sleep problems can be understood as these processes falling out of step.

Why sleep matters

Research links sleep to memory consolidation, learning, emotional processing, immune function and metabolic health. Short-term sleep loss impairs attention, reaction time and mood regulation, and chronic short sleep is associated with higher risks of obesity, diabetes, cardiovascular disease and depression. A 2015 consensus statement recommended that adults regularly get seven or more hours of sleep. See our pages on memory and brain fog for related topics.

Insomnia

Insomnia is the most common sleep disorder. Around a third of adults report some insomnia symptoms, and the DSM-5-TR estimates that about 6–10% meet criteria for insomnia disorder.

What it involves

Insomnia disorder involves dissatisfaction with sleep quantity or quality, with difficulty falling asleep, staying asleep or waking too early, occurring at least three nights a week for at least three months despite adequate opportunity to sleep, and causing significant distress or daytime impairment such as fatigue, poor concentration or irritability. Short-term insomnia, often triggered by stress, illness or life changes, is extremely common and usually resolves.

Why insomnia persists

Psychologist Arthur Spielman's "3P" model describes predisposing factors (such as a tendency to worry or high arousal), precipitating factors (a stressful event that triggers poor sleep) and perpetuating factors (behaviors and thoughts that keep it going after the trigger has passed). Common perpetuating factors include spending long periods in bed awake, napping, irregular schedules, worrying about sleep, and the bed becoming associated with frustration rather than sleep. This is why behavioral treatments are so effective.

Links with mental health

Insomnia frequently co-occurs with depression and anxiety, and research suggests it is not just a symptom but an independent risk factor for developing depression. Treating insomnia directly often improves mood. Racing thoughts at bedtime and rumination are common features.

Sleep Apnea

Sleep apnea is a group of sleep-related breathing disorders in which breathing repeatedly stops or becomes shallow during sleep.

Obstructive sleep apnea

Obstructive sleep apnea (OSA) is by far the most common type. The upper airway repeatedly narrows or collapses during sleep, reducing airflow, lowering oxygen levels and causing brief awakenings the person usually does not remember. A 2019 analysis by Adam Benjafield and colleagues estimated that nearly a billion adults aged 30–69 worldwide may have at least mild OSA, and most cases are undiagnosed. Risk factors include excess weight, male sex, older age, a narrow airway or large tonsils, family history, alcohol and sedative use, and smoking.

Common signs include loud snoring, gasping or choking during sleep, pauses in breathing noticed by a partner, morning headaches, unrefreshing sleep and daytime sleepiness. Untreated OSA is associated with high blood pressure, heart disease, stroke, type 2 diabetes, motor vehicle accidents, and mood and concentration problems.

Central sleep apnea

In central sleep apnea, the brain intermittently fails to send signals to breathe. It is less common and is associated with conditions such as heart failure, stroke, high altitude and some medications. Assessment and treatment are handled by sleep specialists.

Narcolepsy

Narcolepsy is a chronic neurological disorder of the brain's sleep-wake regulation, affecting roughly 1 in 2,000 people. Symptoms usually begin in adolescence or early adulthood, and diagnosis is often delayed by years.

Main features

The core symptom is excessive daytime sleepiness, with an irresistible need to sleep or lapses into sleep during the day. Many people with narcolepsy type 1 also experience cataplexy, sudden brief loss of muscle tone triggered by strong emotions such as laughter, which can range from a sagging jaw to collapse while remaining conscious. Other features include sleep paralysis, vivid hallucinations when falling asleep (hypnagogic) or waking (hypnopompic), and fragmented night-time sleep.

Types and causes

Narcolepsy type 1 is caused by loss of the brain cells that produce hypocretin (also called orexin), a neurotransmitter that stabilises wakefulness. This discovery, made around 1998–2000, transformed understanding of the condition. Type 1 is strongly associated with a particular immune-system gene variant (HLA-DQB1*06:02), and an autoimmune process is thought to be involved. Narcolepsy type 2 involves sleepiness without cataplexy and with normal hypocretin levels; its causes are less clear.

Living with narcolepsy

Management usually combines medication prescribed by a sleep specialist with scheduled short naps, regular sleep routines and practical adjustments at school or work. Driving safety is an important consideration. Narcolepsy can affect mood, education and relationships, and psychological support is often helpful.

Circadian Rhythm Sleep-Wake Disorders

Circadian rhythm sleep-wake disorders occur when the body's internal clock is out of step with the timing of sleep that a person wants or needs. Sleep itself may be normal once it happens, but it occurs at the "wrong" time.

• Delayed sleep-wake phase disorder: a persistent pattern of falling asleep and waking much later than desired, common in adolescents and young adults, who may be mislabelled as lazy.
• Advanced sleep-wake phase disorder: very early sleep and waking times, more common in older adults.
• Non-24-hour sleep-wake rhythm disorder: the internal clock runs on a cycle longer than 24 hours and drifts; it occurs in many totally blind people whose clocks cannot be reset by light.
• Irregular sleep-wake rhythm disorder: sleep broken into several periods across 24 hours, seen in some people with dementia or neurodevelopmental conditions.
• Shift work disorder: insomnia or sleepiness linked to working at night or on rotating shifts.
• Jet lag disorder: temporary misalignment after crossing time zones.

Treatment typically focuses on carefully timed light exposure, consistent schedules and, under medical guidance, other approaches to shift the clock. Our page on remote work and mental health touches on how routines affect sleep timing.

Parasomnias

Parasomnias are unusual behaviors or experiences that occur while falling asleep, during sleep or when waking. They are grouped by the sleep stage in which they occur.

NREM parasomnias

These arise from deep NREM sleep, usually in the first third of the night, and are much more common in children. They include sleepwalking, sleep terrors (sudden episodes of screaming and intense fear with little memory afterwards) and confusional arousals. Many children grow out of them. Triggers include sleep deprivation, irregular schedules, stress, fever and, in adults, alcohol. Safety measures such as securing doors and windows are important.

REM parasomnias

REM sleep behavior disorder involves acting out dreams because the normal paralysis of REM sleep is lost; it mainly affects older adults and is an important early marker of some neurodegenerative conditions. Nightmare disorder involves repeated, distressing, well-remembered dreams that disturb sleep and daytime functioning; it is common in PTSD. Imagery rehearsal therapy, in which people rewrite and rehearse a new version of a recurring nightmare while awake, has research support. Sleep paralysis, a brief inability to move on falling asleep or waking, sometimes with frightening hallucinations, has been reported at least once by around 8% of the general population, according to a 2011 review by Brian Sharpless and Jacques Barber.

Sleep-Related Movement Disorders

Restless legs syndrome (RLS) causes an uncomfortable urge to move the legs that worsens at rest and in the evening and is relieved by movement. It is common, linked to brain iron and dopamine, and often disrupts falling asleep. Periodic limb movement disorder involves repetitive limb movements during sleep that fragment sleep and cause daytime symptoms; many people with RLS also have periodic limb movements. Sleep-related bruxism (teeth grinding) can cause jaw pain, headaches and dental damage, and is associated with stress. Rhythmic movement disorder, such as head banging or body rocking when falling asleep, is common in infants and usually harmless.

Hypersomnia and Insufficient Sleep

Excessive daytime sleepiness has many causes beyond narcolepsy. Idiopathic hypersomnia involves severe sleepiness and long, unrefreshing sleep without a clear cause. Far more commonly, daytime sleepiness reflects insufficient sleep, simply not getting enough sleep because of work, study, caring or screen habits, which is widespread in modern societies. Sleepiness can also result from depression, medical conditions and some medications. The Epworth Sleepiness Scale, developed by Murray Johns in 1991, is a widely used questionnaire for rating daytime sleepiness in clinical settings.

Diagnosis and Sleep Studies

Clinical assessment

Most sleep assessment starts with a detailed history: sleep and wake times, how long it takes to fall asleep, night-time waking, snoring, unusual behaviors, daytime functioning, caffeine, alcohol and medication use, mood and stress. A bed partner's observations are often invaluable. A sleep diary kept for one to two weeks provides a picture of patterns, and questionnaires such as the Insomnia Severity Index and Epworth Sleepiness Scale help measure severity.

Sleep studies

• Polysomnography (PSG): an overnight study, usually in a sleep laboratory, recording brain waves (EEG), eye movements, muscle activity, heart rhythm, breathing, oxygen levels and limb movements, often with video. It is used to diagnose sleep apnea, narcolepsy, REM sleep behavior disorder and other conditions.
• Home sleep apnea testing: a simplified recording of breathing and oxygen levels at home, used for suspected obstructive sleep apnea in suitable adults.
• Multiple Sleep Latency Test (MSLT): a series of daytime nap opportunities after an overnight study, measuring how quickly a person falls asleep and whether REM occurs early; used in diagnosing narcolepsy.
• Actigraphy: a wrist-worn device that estimates sleep and wake patterns over days or weeks, useful for circadian rhythm disorders and insomnia.

Sleep studies are not usually needed to diagnose insomnia, which is based on the clinical history. Consumer sleep trackers can be interesting but are less accurate than clinical tools and sometimes increase anxiety about sleep.

Treatment Approaches

Treatment depends on the specific disorder. The overview below describes general approaches; individual treatment decisions are made with a doctor or sleep specialist.

Cognitive behavioral therapy for insomnia (CBT-I)

CBT-I is recommended as the first-line treatment for chronic insomnia in adults by the American College of Physicians (2016) and other bodies, because it is effective and its benefits tend to last after treatment ends. Core components include:

• Sleep restriction: temporarily limiting time in bed to match actual sleep time, building stronger sleep pressure, then gradually extending it.
• Stimulus control: using the bed only for sleep and sex, going to bed only when sleepy, and getting up if unable to sleep, to rebuild the bed-sleep association.
• Cognitive therapy: addressing worries and unhelpful beliefs about sleep, such as catastrophising about the effects of one bad night.
• Relaxation techniques such as progressive muscle relaxation.
• Sleep hygiene education.

CBT-I is delivered individually, in groups or through digital programmes, several of which have research support. See cognitive behavioral therapy for background.

Medication

Medications are used for some sleep disorders, including short-term management of insomnia, narcolepsy and some movement disorders. They have benefits and risks, including next-day drowsiness, falls in older adults, and dependence with some types, and many are intended for short-term use only. Over-the-counter sleep aids and supplements also carry side effects and interactions. Decisions about any medication or supplement should be made with a doctor or pharmacist; this page does not give medication advice.

Treatments for sleep apnea

Continuous positive airway pressure (CPAP), in which a mask delivers air pressure that keeps the airway open, is the standard treatment for moderate to severe obstructive sleep apnea and is very effective when used consistently, though many people find it hard to tolerate at first. Alternatives include custom oral appliances that move the lower jaw forward, positional therapy, weight loss, surgery in selected cases and, for some people, implanted nerve stimulation devices. Psychological support can help people adapt to CPAP.

Other approaches

Other treatments include carefully timed light exposure for circadian rhythm disorders, imagery rehearsal therapy for nightmares, safety measures for parasomnias, and treating underlying medical or mental health conditions. Treating co-occurring conditions such as depression, anxiety and PTSD often improves sleep, and vice versa.

Sleep Hygiene and Prevention

"Sleep hygiene" refers to habits and environmental factors that support good sleep. On their own, these measures are usually not enough to treat chronic insomnia or other sleep disorders, but they help maintain healthy sleep and support other treatments. Our dedicated sleep hygiene page goes into more detail.

Helpful habits

• Consistent timing: going to bed and getting up at similar times every day, including weekends.
• Morning light and daytime activity: natural light early in the day and regular exercise support the circadian rhythm.
• Caffeine and alcohol: limiting caffeine in the afternoon and evening, and being aware that alcohol fragments sleep later in the night.
• Wind-down routine: a calming pre-bed period, with dimmer light and fewer stimulating activities. Bright screens late at night can delay the body clock and keep the mind alert.
• Bedroom environment: cool, dark and quiet where possible.
• Managing worry: setting aside time earlier in the evening to note concerns, or practices such as mindfulness meditation and breathing exercises.

Across the lifespan

Children and teenagers need more sleep than adults, and adolescents' body clocks naturally shift later, which is why some researchers advocate later school start times. Older adults tend to sleep more lightly and wake earlier; new or worsening sleep problems in later life are worth discussing with a doctor because they can signal treatable conditions. Shift workers benefit from planning sleep periods, light exposure and workplace policies that support recovery.

When to seek help

See a doctor if sleep problems last more than a few weeks and affect daytime life; if you snore loudly and someone has noticed gasping or pauses in your breathing; if you fall asleep unintentionally during the day or while driving; if you act out dreams or have frequent unusual night-time behaviors; or if sleep problems come with low mood, anxiety or thoughts of self-harm. In a crisis, see our crisis resources.

Conclusion

Sleep disorders are common, varied and often underdiagnosed, yet many are highly treatable. Understanding normal sleep, recognising the main types of disorder, and knowing when to seek help are important steps. Because sleep and mental health are so closely linked, improving sleep can support emotional wellbeing, and addressing stress, anxiety and depression can improve sleep in turn. A doctor or sleep specialist can help identify the cause of persistent sleep problems and recommend an evidence-based plan.