Delirious describes a confused, disoriented mental state where someone can't think clearly or tell what's real. When you have a high fever, you might become delirious, seeing things that aren't there or saying strange things that don't make sense. A delirious person might not recognize their own bedroom or might think they're somewhere completely different.

This confusion happens because illness, extreme exhaustion, or dehydration affects how the brain works. Doctors take delirium seriously because it signals that something is wrong with the body. A delirious patient in a hospital might try to get out of bed thinking they need to catch a bus, when they're actually supposed to be resting.

The word can also describe wild excitement or joy that makes someone act a little crazy. When your team wins the championship, fans might become delirious with joy, screaming and jumping around. In this sense, being delirious means you're so overwhelmed with emotion that you lose your normal composure. A crowd might go delirious when their favorite singer takes the stage.

Related word: delirium is the noun form, describing the state itself rather than the person experiencing it.