What is delirium and what causes it?

Delirium refers to a rapidly developing and severe confusion accompanied by altered consciousness and an inability to focus. It's the most common complication of hospitalization among people ages 65 and over: 20% of those admitted to hospitals, up to 60% of those who have certain surgeries, and almost 80% of those treated in ICUs develop delirium. Illicit and prescription drugs and even certain over-the-counter medications can cause delirium. Delirium can also happen with any severe infection, especially those with high fever or affect the brain. Delirium is also a feature of psychosis and some other mental health disorders.