Insomnia may be classified according to the duration of difficulty sleeping into 3 groups: short-term insomnia disorder (< 3 months), chronic insomnia disorder (sleep disturbances that occur at least three times per week for > 3 months), and other insomnia disorder.

• Insomnia may be classified according to the duration of difficulty sleeping by the 3rd Edition of International Classification of Sleep Disorder (ICSD-3) into 3 groups:^[1]
  • Short-term insomnia disorder (< 3 months)
  • Chronic insomnia disorder (sleep disturbances that occur at least three times per week for > 3 months)
  • Other insomnia disorder (sleep disturbances that do not meet the criteria for aforementioned groups)

• Historically, Insomnia was classified according to the presence of a comorbid condition (primary versus secondary insomnia) and the presence of an organic cause (organic vs non-organic). Then primary insomnia further classified by the 2nd Edition of International Classification of Sleep Disorder into:
  • Psychophysiologic
  • Idiopathic
  • Paradoxical (sleep-state misperception)
• However, due to the difficulty in the distinction of associations with comorbid diseases, the uncertain direction of causality between insomnia and comorbid diseases, and insufficient treatment of the sleep disturbance in patients with secondary insomnia (this classification resulted in focusing the treatment of comorbid condition while ignoring the treatment of insomnia), ICSD-3 bring together all insomnia diagnoses (ie, “primary” and “comorbid”) under the same roof, which is chronic insomnia disorder.^[2]