Which disorder's diagnostic criteria specify a duration of at least three months with symptoms occurring at least three nights per week?

• A. Circadian Rhythm Sleep-Wake Disorders
• B. Breathing-Related Sleep Disorders
• C. Insomnia Disorder
• D. Parasomnias

Answer: (C)

The key idea here is the duration criterion for Insomnia Disorder. In DSM-5, insomnia is diagnosed when a person has difficulty initiating sleep, maintaining sleep, or waking up too early, at least three nights per week, for a minimum of three months, and this sleep problem causes distress or impairment despite adequate opportunity to sleep. This three-times-per-week, three-month pattern is what distinguishes a persistent insomnia problem from shorter or situational sleep difficulties. The other sleep categories don’t hinge on this same duration pattern: circadian rhythm sleep-wake disorders center on a misalignment with the 24-hour day rather than a fixed frequency over months; breathing-related sleep disorders involve respiratory problems during sleep; and parasomnias involve abnormal behaviors or events during sleep. So the described duration fits insomnia disorder exactly.