World Health Organization (WHO )

The organization defines insomnia as a problem with falling asleep, remaining asleep, and/or nonrestorative sleep that occurs at least three nights per week and is associated with distress or functional impairment.

American Psychiatric Association (APA) [6]

The association uses the diagnostic term “insomnia disorder” whether it occurs as an independent condition or is comorbid with another condition (e.g., medical, mental, or another sleep disorder). The APA specifies a duration criteria of at least 3 months and a frequency of at least three nights per week. The diagnosis is made when the primary problem is dissatisfaction with sleep quantity or quality related to trouble initiating and/or maintaining sleep and/or early-morning awakening with inability to return to sleep. Further, the sleep complaint must be associated with significant distress and impairment in important areas of functioning (e.g., occupational, educational, academic, behavioral, social, etc.) and is not due to another medical, psychiatric, or sleep disorder.

International Classification of Sleep Disorders (ICSD) , Third Edition

The book is published by the American Academy of Sleep Medicine (AASM) and defines insomnia as “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.” The three diagnostic categories listed for insomnia, include chronic insomnia disorder, short-term insomnia disorder, and other insomnia disorder. In order to meet diagnostic criteria for chronic insomnia disorder, the sleep disturbance(s) and accompanying daytime impairment must be present at least three times a week for at least 3 months. Patients reporting insomnia symptoms that do not reach the frequency and/or duration thresholds, but do exhibit significant dissatisfaction with their sleep and/or waking impairment , are classified as having short-term insomnia disorder. Individuals failing to meet criteria for short-term insomnia, but with clinically significant sleep disturbance or daytime impairment, may be classified with other insomnia disorder.

Initial-/early-/sleep-onset insomnia

Middle-/sleep- maintenance insomnia

Refers to difficulty with frequent or prolonged awakenings during sleep period

Terminal/late insomnia

Sleep-onset latency (SOL)

It is the length of time to transition from wakefulness to sleep at the beginning of the sleep period.

Wake after sleep onset (WASO)

It is the total amount of time spent awake after the initiation of sleep and before final awakening.

Final awakening (FA)

It is the time at which the individual awakens from his/her sleep period and no longer returns to sleep.

Time out of bed (TOB)

It is the time at which the individual physically gets out of bed at the end of their sleep period which may or may not be the same as their final awakening.

It is the time from when a person goes to bed with the intention of going to sleep until the time he/she gets up for the day at the end of their sleep period.

Total sleep time

It is the amount of actual sleep time in a sleep period that is equal to time in bed minus time awake (SOL + WASO + time between FA and TOB).

It is the proportion of time in bed that is actually spent sleeping. Mathematically, it is calculated by dividing total sleep time by time in bed.

It is a relatively short period of sleep generally obtained at a time separate from the major sleep period.

This is a circadian rhythm disorder that is common in adolescents and young adults. Individuals have “night-owl” tendencies in which their sleep onset can be delayed until 2 a.m. or later. If allowed to sleep late (often as late as 3 p.m.), sleep deprivation does not occur. Typically, sleep deprivation occurs when there is a misalignment between the individual’s desire for earlier bedtimes and wake times and their body’s natural tendency for later bed- and wake times. Earlier wake-up times can lead to daytime sleepiness and impaired work and school performance.

This is a circadian rhythm disorder that is common in older adults. This disorder is identified by regular early-evening bedtimes (e.g., 6 p.m.–9 p.m.) and early-morning awakenings (e.g., 2 a.m.–5 a.m.). People with advanced sleep phase syndrome are “morning larks” and often complain of early-morning awakening or insomnia as well as sleepiness in the late afternoon or early evening.