A sudden decline in attention, focus, cognition, and perception developing over hours or days. Not to be confused with dementia.
Example: An elderly alcoholic man who was asymptomatic yesterday mumbles, picks at invisible objects, seems intensely fearful, and misidentifies you as his relative.
Grinnell, R. (2008). Delirium. Psych Central. Retrieved on May 22, 2015, from http://psychcentral.com/encyclopedia/2008/delirium/