Delirium is an altered state of consciousness in which a person is restless, excitable, hallucinating, and is only partly aware of his or her surroundings. It is seen in high fever, poisoning, drug withdrawal, disorders of metabolism, and organ failure. Sedatives and reassurance are basic measures.

Delirium tremens is a specific delirium to due to acute alcohol withdrawal in alcoholism. It occurs within days of abstinence and is often precipitated by injury, surgery, or imprisonment. The sufferer becomes restless, disoriented, extremely anxious, and tremulous; fever and profuse sweating are usual. Characteristically, hallucinations of insects or animals cause abject terror. Constant reassurance, sedatives, and quiet and well-lit surroundings are appropriate measures until the episode is over. Treatment of dehydration and reduction of high fever may be necessary, though fatalities do occur.