Insomniamay be characterized based on its duration. Acute insomnia is brief and often happens because of life circumstances (for example, when you can't fall asleep the night before an exam, or after receiving stressful or bad news). Many people may have experienced this type of passing sleep disruption, and it tends to resolve without any treatment. Chronic insomnia is disrupted sleep that occurs at least three nights per week and lasts at least three months. Chronic insomnia disorders can have many causes. Changes in the environment, unhealthy sleep habits, shift work, other clinical disorders, and certain medications could lead to a long-term pattern of insufficient sleep. People with chronic insomnia may benefit from some form of treatment to help them get back to healthy sleep patterns. Chronic insomnia can be comorbid, meaning it is linked to another medical or psychiatric issue, although sometimes it's difficult to understand this cause and effect relationship.

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