Sleep and sleep disorders

Last updated: November 22, 2023

Summarytoggle arrow icon

Sleep is a physiologically recurring state of rest characterized by relative suspension of consciousness and inaction of voluntary muscles. It is regulated by the circadian rhythm and usually consists of 4–5 sleep cycles that include three stages of non-rapid eye movement sleep (NREM sleep) and one stage of rapid eye movement sleep (REM sleep). Sleep disorders can be grouped into primary disorders (i.e., due to an intrinsic disorder of the sleep-wake cycle) and secondary disorders (i.e., due to an underlying medical condition). Primary sleep disorders are further divided into dyssomnias and parasomnias. Symptoms include difficulty falling asleep, difficulty remaining asleep, or abnormal behavior during sleep. Environmental factors (e.g., long working hours, irregular sleep schedules, alcohol consumption) can also lead to sleep loss. Symptoms include excessive daytime sleepiness and cognitive impairment. Treatment of sleep disorders and sleep loss may include sleep hygiene practice, phototherapy, and sedative pharmacotherapy.

Narcolepsy, restless legs syndrome, and obstructive sleep apnea are discussed in separate articles.

Sleep physiologytoggle arrow icon

Normal sleep cycle [1]

Normal sleep phases [1][3]

Sleep phases characteristics
Phase Description EEG findings Sleep-phase-specific disorders
  • Alert
  • Beta waves (> 13 Hz) with the lowest amplitude
  • Eyes closed
  • Alpha waves (8–13 Hz)

NREM sleep

Stage N1
  • Lightest stage of sleep
  • 5–10% of total sleep time
  • Characterized by hypnic jerks: spontaneous myoclonic contractions associated with a sensation of twitching or falling
  • Theta waves (4–7 Hz)
Stage N2
  • Deeper sleep compared to N1 sleep
  • 45–55% of total sleep time
  • Theta waves (4–7 Hz)
  • Sleep spindles: short bursts of EEG waves with a frequency of 12–14 Hz [4]
  • K-complexes: high amplitude, diphasic, frontocentral slow waves
  • Teeth grinding (bruxism) most commonly occurs during N2 sleep.
Stage N3
  • Slow-wave sleep (deepest sleep)
  • 10–25% of total sleep time
  • The percentage of N3 stage decreases with age.
  • The length of N3 stages decreases over the course of the night.
  • High waking threshold
  • Delta waves (EEG) (0–4 Hz) with the highest amplitude

REM sleep

  • General characteristics
    • 18–25% of total sleep time
    • High dream activity
    • The percentage of REM sleep decreases with age.
    • The duration and the proportion of REM sleep in relation to NREM sleep increases over the course of the night.
    • High waking threshold
  • Electromyographic activity
  • Autonomic activity
  • REM sleep latency
    • Period of time between the onset of sleep and the first REM episode
    • Typically lasts 90–120 minutes in a healthy person

“For BETTER (read “beta”) WAVES, Ask The Silent Surfer Dozing at the Beach:” Beta waves while awake; Alpha waves with eye closure; Theta waves during N1; Sleep spindles during N2; Delta waves during N3; Beta waves during REM sleep).

“I saw the t(w)ooth fairy fleeing and the three little pigs peeing:” teeth grinding occurs during N2 stage and bedwetting during N3 stage NREM sleep.

Classification of sleep disorderstoggle arrow icon

Primary sleep disorders


Parasomnias [6]

Sleep-related movement disorders [7]

Secondary sleep disorders

  • See “Sleep-phase-specific disorders” in “Sleep physiology” section above.

Circadian rhythm sleep-wake disorderstoggle arrow icon

Common features of circadian rhythm sleep-wake disorders

Delayed sleep phase disorder

Advanced sleep phase disorder

Jet lag disorder

Shift-work disorder

Non-24 hour sleep-wake disorder [10]

Insomnia disordertoggle arrow icon

Overview [11][12][13]

  • Definition: a dissatisfying quantity or quality of sleep that leads to some form of daytime dysfunction
  • Epidemiology: most common sleep-wake disorder (global prevalence ∼ 10%)
  • Etiology: complex and not fully understood
    • Predisposing factors include:
      • A chronic state of cognitive and physiological hyperarousal
      • Medical comorbidities, including mood and anxiety disorders [12]
    • Precipitating (acutely triggering) factors: e.g., stressful events (acute or chronic)
    • Perpetuating factors: e.g., poor sleep hygiene
  • Clinical features include:
    • Difficulty falling asleep, maintaining sleep, or early morning awakening
    • Nonrefreshing sleep
    • Impaired daytime functioning
      • Fatigue
      • Cognitive impairment
      • Mood disturbance
      • Difficulty with social, academic, or occupational functioning
  • Potential health consequences
    • Development of mood disorders and increased risk of suicide [13]
    • Workplace injuries
    • Reduced quality of life

Insomnia is the most common sleep-wake disorder, affecting ∼ 10% of the population worldwide. Prevalence is higher in women, shift workers, and people with physical or mental disorders or disabilities.

Diagnosis [11][12][13][14]

Clinical assessment

Obtain a detailed clinical history, including symptoms and contributing factors; the Insomnia Severity Index or the Pittsburgh Sleep Quality Index are commonly used standardized assessment tools.

  • Sleep-related symptoms
    • Inquire about sleeping habits and bedtime routine.
    • Determine symptom onset, triggers, and interventions already tried.
    • Identify nighttime symptoms and assess their frequency and pattern. [13]
      • Difficulty falling asleep, staying asleep, and/or waking early
      • Behaviors during sleep (including snoring, witnessed apneas, and leg kicking)
    • Ask about daytime impaired functioning and/or sleepiness.
  • Medical and psychiatric history should include: [13][15]
    • Comorbid conditions and associated symptoms that could interfere with sleep
    • Medication use (prescription and over-the-counter) and the time at which medications are taken
    • Alcohol consumption, use of stimulants (e.g., nicotine, caffeine), and sedatives (e.g., opioids, benzodiazepines)
    • Occupation, school, and working hours
  • Physical exam: Check BMI, neck circumference, and airway to evaluate for OSA.

Medications that may interfere with sleep include decongestants (e.g., pseudoephedrine or phenylephrine), bronchodilators (e.g., albuterol or theophylline), antidepressants, antihypertensives (e.g., beta blockers, calcium channel blockers, diuretics), glucocorticoids, sedatives, and hypnotics.

Diagnostic criteria for insomnia disorder

The most common sets of criteria are the International Classification of Sleep Disorders (ICSD-3) and the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), which are largely consistent with one another.

Diagnosis of insomnia disorder [12][14]
ICSD-3 criteria [6] DSM-5 criteria [16]

Nighttime symptoms

(presence of ≥ 1 feature)

  • Difficulty initiating sleep [12]
  • Difficulty maintaining sleep [12]
  • Early-morning awakening with inability to return to sleep
  • Difficulty going to bed at an appropriate time
  • Need for intervention from a parent or caregiver to fall asleep
  • Difficulty initiating sleep (initial or sleep-onset insomnia) [12]
  • Difficulty maintaining sleep (middle or sleep-maintenance insomnia), i.e., frequent or prolonged awakening from sleep [12]
  • Early-morning awakening with inability to return to sleep (late or sleep-offset insomnia)

Daytime symptoms

(presence of ≥ 1 feature)

  • Fatigue or daytime sleepiness [12]
  • Disturbed mood or behavior (e.g., irritability, impulsivity, or aggression)
  • Impaired cognition (e.g., problems with attention, concentration, or memory)
  • Reduced motivation and/or energy
  • Prone to errors or accidents
  • Impaired functioning in a social, occupational, or academic capacity
  • Clinically significant distress or impairment in at least one area of functioning (e.g., social, occupational, academic)
Additional considerations
  • Symptoms occur despite adequate time and environment for sleep.
  • Symptoms cannot be attributable to:
    • Use of a substance or medication
    • Medical or psychiatric comorbidities or other sleep disorders [12]


  • Symptoms occur ≥ 3 times per week
  • Symptoms occur ≥ 3 times per week
    • Episodic insomnia: 1–3 months
    • Persistent insomnia: ≥ 3 months
    • Recurrent insomnia: Patient meets criteria for episodic insomnia at least 2 times within 1 year.

Additional studies [13]

Diagnostic studies are not required to diagnose insomnia, but they may be useful in select patients:

Management [17][18][19]

Approach [20]

Cognitive behavioral therapy is the first-line treatment for chronic insomnia. [17]

Nonpharmacological management [15][19]

There are multiple nonpharmacological interventions that can improve sleep and their impact is greater when used in combination.

Behavioral and cognitive therapies for insomnia [15][19]
Goal Techniques

Sleep hygiene

  • Avoid factors that may trigger or exacerbate insomnia.
  • Use the bed/bedroom only for sleep or sex.
  • Avoid alcohol, caffeine, and nicotine close to bedtime.
  • Exercise regularly, but not within 3–4 hours before bedtime.
  • Avoid daytime naps.
  • Avoid large meals and fluid intake in the evenings.
  • Avoid bright lights (including electronic screen use) before bedtime.
Stimulus control
  • Reestablish the association between bed/bedroom and sleep.
  • Establish a consistent sleep/wake schedule.
  • Discourage engaging in other activities in bed.
  • Maintain a regular sleep/wake cycle (wake up at the same time every day, avoid naps).
  • Wait to go to bed until feeling sleepy.
  • If unable to fall asleep within 20 minutes:
    • Leave the bedroom to sit somewhere quiet.
    • Return only when sleepy.
Cognitive therapy
  • Identify and reframe dysfunctional beliefs about sleep.
  • Counseling/psychoeducation
  • Paradoxical intention
    • Cognitive behavior therapy for patients with chronic insomnia aimed at reducing the anxiety and stress surrounding being unable to sleep
    • In this technique, the patient is advised to remain awake as long as possible, but otherwise follow good sleep hygiene practices (e.g., avoiding stimulants close to bedtime, exercising, sunlight exposure during the day and darkness at night).
  • Journaling, including thought records

Sleep restriction

  • Advise patient to restrict time spent in bed to only the time spent sleeping and increase gradually.
Relaxation training
  • Reduce physical and cognitive arousal and anxiety.

CBT-I combines cognitive therapy, stimulus control, and sleep restriction therapy, possibly with the addition of relaxation training. [15]

Avoid sleep restriction in patients with seizure disorders or bipolar disorders, as it can lower the threshold for seizures or precipitate manic episodes. [13]

Patients using sleep restriction to manage insomnia should avoid driving and operating heavy machinery. [13]

Pharmacotherapy for insomnia [13][20][21]

Benzodiazepines carry a high risk of addiction and should therefore only be considered for short-term use.

Short-acting agents are useful for sleep-onset insomnia; longer-acting agents are useful for sleep-maintenance insomnia but increase the risk of next-day effects.

Overview of pharmacotherapy for insomnia [13][18][21]

Class Agents

Cautions [11][13][17]

Benzodiazepine receptor agonists

  • Dose-dependent daytime sedation and memory, cognitive, and psychomotor impairment
  • Complex sleep-related behaviors (e.g., sleepwalking)
  • Addictive potential
Melatonin receptor agonist
  • Adverse effects include headaches, nausea, fatigue and daytime sedation.
  • Avoid in patients with hepatic disease and those with severe sleep apnea.
Orexin receptor antagonist
  • May cause daytime sedation
  • Addictive potential (avoid in patients with a history of substance use disorder)
  • Not recommended for patients with severe hepatic disease
Tricyclic antidepressants
Others (not routinely recommended)
  • These medications are commonly prescribed but are not approved for insomnia by the FDA.

Avoid the use of benzodiazepine receptor agonists as a first-line medication for the treatment of insomnia in older adults and in patients with a history of substance use disorder or drug dependence. [11][21]

Inpatient managementtoggle arrow icon

Inpatients frequently experience insomnia due to disruptive changes in routine and the fact that the hospital environment is not always conducive to sleep. [22][23][24]

Carefully consider adverse effects and medication interactions before prescribing medications for insomnia.

Sedatives and hypnotics are often overprescribed to inpatients. Clinicians should avoid them if possible and, when necessary, they should be prescribed carefully, after weighing the risk of potential adverse events and pharmacological interactions. [22]

Hypersomnolence disordertoggle arrow icon


Clinical features

  • Excessive sleep (with decreased sleep quality)
  • Difficulty awakening from sleep
  • Sleep inertia (impaired alertness or excessive fatigue after waking)
  • Automatic behaviors (with no memory of the episode after waking)

DSM-5 diagnostic criteria [26]

  • Excessive sleepiness despite ≥ 7 hours of sleep with at least one of the following:
    • Recurrent periods of sleep on the same day
    • > 9 hours of sleep that is nonrestorative
    • Impaired alertness after awakening
  • Symptoms occur ≥ 3 days/week for ≥ 3 months
  • Symptoms cause functional impairment or distress
  • Symptoms not caused by an underlying substance or medication use
  • Symptoms occur despite having enough time to sleep
  • No underlying or coexisting psychiatric or medical disorder that explains symptoms


Parasomniastoggle arrow icon

Sleepwalking disorder

Sleep terror disorder

Nightmare disorder

REM sleep behavior disorder

Other parasomnias

“I REMember my NIGHTMARE, and there were NO memorable TERRORists:” Nightmare disorder occurs during REM sleep and the experience is remembered, while sleep terror disorder occurs during non-REM sleep and is not remembered.

Periodic limb movement disordertoggle arrow icon

  • Definition: : a condition characterized by periodic limb movements of sleep (PLMS) that is not associated with any other disease
  • Etiology: unknown
  • Pathophysiology: idiopathic malfunction of the dopaminergic system
  • Clinical features
    • Frequent and stereotypic involuntary movement in the legs (e.g., flexion and extension of the toes, ankles, knees, and hips) and/or in the arms (less common) during sleep.
    • Clinically significant sleep disturbance or functional impairment not explained by any other disorder
  • Diagnostics: Polysomnography
  • Treatment: benzodiazepines, dopaminergic agents, OR antiepileptics drugs (e.g, gabapentin)

Age-related sleep changestoggle arrow icon

Normal changes in sleep architecture occur with aging, and include:

  • Decreased total sleep time [34]
    • Decreased time spent in deep sleep and REM sleep
    • Increased sleep latency
    • More frequent nighttime awakenings that are likely multifactorial (e.g., due to nocturia, pain, and/or less time spent in deeper stages of sleep)
  • Advanced circadian rhythms resulting in earlier bedtimes and thus morning awakenings [34]

Sleep deprivationtoggle arrow icon

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Referencestoggle arrow icon

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