What is Insomnia?
Insomnia is a sleep disorder characterized by difficulty initiating sleep, difficulty maintaining sleep, or waking up too early, occurring despite adequate opportunity for sleep, and resulting in daytime impairment such as fatigue, concentration problems, or mood disturbance. 1
Core Diagnostic Criteria
The American Academy of Sleep Medicine defines insomnia disorder using three essential components that must all be present 1:
A. Nighttime Sleep Complaint (at least one of the following):
- Difficulty falling asleep (prolonged sleep-onset latency)
- Difficulty staying asleep (frequent or prolonged awakenings)
- Waking up too early and unable to return to sleep
- Sleep that is chronically nonrestorative or poor quality 1
B. Adequate Sleep Opportunity:
- The sleep difficulty must occur despite having adequate opportunity and circumstances for sleep 1
- This distinguishes insomnia from sleep deprivation due to external factors (work schedules, caregiving responsibilities, etc.)
C. Daytime Consequences (at least one required):
- Fatigue or malaise
- Impaired attention, concentration, or memory
- Social, vocational, or academic dysfunction
- Mood disturbance or irritability
- Daytime sleepiness
- Reduced motivation, energy, or initiative
- Proneness to errors or accidents at work or while driving
- Tension headaches or gastrointestinal symptoms related to sleep loss
- Concerns or worries about sleep 1
Duration Classifications
The American Psychiatric Association's DSM-5 defines insomnia disorder (chronic insomnia) as occurring at least 3 nights per week for 3 months or more 1. Earlier terminology distinguished:
- Transient insomnia: Lasting from one night to 2 weeks, typically in response to stress or anxiety-provoking events 1
- Acute insomnia: Lasting up to one month 1
- Chronic insomnia: Persisting for at least one month (older criteria) or 3 months (current DSM-5 criteria) 1
Important Distinction: Symptom vs. Disorder
The term "insomnia" is used in two contexts 1:
- As a symptom: Sleep difficulty that may occur transiently or as part of another condition
- As a disorder: A specific diagnosis meeting all three criteria above (sleep complaint + adequate opportunity + daytime impairment)
When clinicians use the term "insomnia" without qualification, they typically refer to insomnia disorder, not just the symptom. 1
Epidemiology and Risk Factors
- Insomnia symptoms occur in 33-50% of adults 1
- Insomnia disorder with distress or impairment affects 10-15% of adults 1
- Specific insomnia disorders meeting full diagnostic criteria affect 5-10% of adults 1
- Consistent risk factors include female sex, increasing age, comorbid medical or psychiatric conditions, shift work, and lower socioeconomic status 1
Common Clinical Pitfall
A critical diagnostic error is treating insomnia as simply "trouble sleeping" without assessing for adequate sleep opportunity and daytime consequences. 1 For example, a shift worker who cannot sleep during the day due to noise and light exposure does not have insomnia disorder—they have insufficient sleep opportunity. Similarly, someone who reports poor sleep but has no daytime impairment does not meet criteria for insomnia disorder. 1
Comorbid Conditions
Insomnia frequently occurs alongside other conditions rather than in isolation 1:
- Sleep-related breathing disorders (sleep apnea)
- Circadian rhythm sleep disorders
- Sleep-related movement disorders (restless legs syndrome)
- Psychiatric disorders (depression, anxiety)
- Medical conditions (chronic pain, hyperthyroidism, neurological diseases) 1, 2, 3
The presence of comorbid conditions does not exclude the diagnosis of insomnia disorder—both conditions should be identified and treated. 1