Jun 01, 2026

What Is Insomnia? Definition, Types, and Causes

Quick answer: Insomnia is a sleep disorder defined by persistent difficulty falling asleep, staying asleep, or waking too early — despite adequate opportunity to sleep — that causes daytime impairment. When it occurs at least three nights a week for three months or more, it is classified as chronic insomnia disorder.

Insomnia is the most common sleep disorder, affecting roughly 10–15% of adults chronically and up to 30% at any given time. Understanding exactly what it is — and isn't — is the first step toward treating it effectively.

Key takeaways

Insomnia = difficulty with sleep onset, maintenance, or early waking that causes daytime impairment.
Chronic insomnia disorder: symptoms ≥3 nights/week, ≥3 months, with daytime impact.
Short-term insomnia: same symptoms but lasting under 3 months, usually tied to a stressor.
Insomnia is a disorder of hyperarousal — the brain is too alert, not incapable of sleep.
CBT-I is the first-line treatment; sleep medications are second-line.

The clinical definition of insomnia

The American Academy of Sleep Medicine (AASM) defines insomnia disorder as a self-reported dissatisfaction with sleep quality or quantity, with one or more of these symptoms despite adequate opportunity and circumstances for sleep:

Difficulty initiating sleep
Difficulty maintaining sleep (frequent or prolonged awakenings)
Early morning awakening without being able to return to sleep

The sleep disturbance must cause clinically significant distress or impairment in social, occupational, or other areas of functioning. For chronic insomnia disorder, these symptoms must occur at least three nights per week and have been present for at least three months.

Types of insomnia

Chronic insomnia disorder

The most persistent form: symptoms ≥3 nights/week for ≥3 months with daytime consequences. Approximately 10–15% of adults meet these criteria. It is maintained by learned arousal cues, cognitive hyperarousal, and behavioral patterns — independent of any original trigger.

Short-term (acute) insomnia

Insomnia lasting less than 3 months, typically linked to an identifiable stressor (life event, illness, job change). For many people it resolves on its own; for some it evolves into chronic insomnia if maintaining behaviors take hold.

Sleep-onset vs. sleep-maintenance insomnia

Some people struggle primarily to fall asleep; others fall asleep easily but wake in the night or early morning. Many have both. These subtypes often point to different underlying drivers (anxiety vs. early circadian timing, for example).

What insomnia is not

Not simply "not enough sleep": a person with insomnia would sleep more if they could. The defining feature is inability to sleep despite adequate opportunity.
Not a character flaw: insomnia involves measurable neurobiological hyperarousal — not weakness or lack of effort.
Not the same as sleep deprivation: sleep deprivation results from insufficient time allotted for sleep; insomnia is present even when sufficient time is available.

What causes insomnia to persist

The Spielman 3P model is the most accepted framework: predisposing factors (genetics, anxious temperament, female sex), precipitating factors (stressors, illness, shift work), and perpetuating factors (spending too long in bed, napping, worry about sleep). The perpetuating factors are what turn short-term insomnia into a chronic condition — and they are the primary targets of CBT-I.

How insomnia is treated

The AASM recommends CBT-I (cognitive behavioral therapy for insomnia) as the first-line treatment for chronic insomnia disorder. Pharmacological options are second-line, short-term tools. Sleep hygiene improvements are an essential component of any approach.

If insomnia is significantly affecting your life, Circady's sleep assessment can help identify the most relevant behavioral drivers and match you with the right CBT-I approach.

Frequently asked questions

What is insomnia?

Insomnia is a sleep disorder characterized by difficulty falling asleep, staying asleep, or waking too early — despite having the chance to sleep — that causes daytime impairment such as fatigue, mood disturbance, or difficulty concentrating.

What are the types of insomnia?

The main clinical types are chronic insomnia disorder (≥3 nights/week for ≥3 months) and short-term insomnia (under 3 months). By symptom subtype: sleep-onset insomnia and sleep-maintenance insomnia.

How common is insomnia?

About 10–15% of adults have chronic insomnia disorder. Up to 30% experience insomnia symptoms at any given time. It is more common in women, older adults, and people with anxiety or depression.

What causes insomnia?

Insomnia is typically triggered by a stressor and then maintained by learned behaviors and thoughts (spending too long in bed, anxiety about sleep). Genetics, gender, and age also influence susceptibility.

Can insomnia go away on its own?

Short-term insomnia often resolves once the precipitating stressor is removed. Chronic insomnia rarely resolves without targeted treatment — CBT-I has the strongest evidence for lasting improvement.

References

American Academy of Sleep Medicine. International Classification of Sleep Disorders, 3rd edition (ICSD-3). Darien, IL: AASM; 2014.
Morin CM, LeBlanc M, Daley M, et al. Epidemiology of insomnia: prevalence, self-help treatments, consultations, and determinants of help-seeking behaviors. Sleep Medicine, 2006. pubmed.ncbi.nlm.nih.gov/16517202
Spielman AJ, Caruso LS, Glovinsky PB. A behavioral perspective on insomnia treatment. Psychiatric Clinics of North America, 1987.

Medically reviewed by Dr. Alf Fischbein, MD — June 1, 2026.

This article is for educational purposes only and is not a substitute for professional medical advice. If you think you have insomnia, consult a healthcare provider for a proper evaluation.