Insomnia is an inability to sleep well. A person with insomnia may have difficulty falling asleep or staying asleep, or may wake up earlier than desired, resulting in symptoms such as daytime fatigue, irritability, and poor memory.

Short-term (temporary) insomnia lasting from a day to a month is very common. An occasional restless night may be caused by a period of emotional distress or sleeping in an unfamiliar bed. Ongoing (chronic) insomnia lasts a month or more and can cause significant distress. Chronic insomnia can be caused by many other conditions, such as depression, chronic pain, medications, poor sleep habits, or even worrying about sleeping.

Treatment for insomnia focuses on the cause of the inability to sleep well. Insomnia caused by an underlying medical problem usually goes away once the problem is treated. Treatment options include minor lifestyle changes, behavioural therapy, and short-term use of medications.