With luck, you'll never witness delirium, but it's critical to know about. Delirium is a common side effect of physical stress caused by things like infection (a urinary tract infection, for example), dehydration, pain, or the stresses of hospitalization. Older adults with dementia are especially vulnerable to delirium -- and it's an important clue to many correctable problems.
Signs of delirium: Your loved one appears to undergo a drastic decline in condition -- greater mental confusion than usual, an apparent worsening of memory, hallucinating, unusual agitation or drowsiness, unintelligible speech, or difficulty focusing (any of these, not necessarily all).
What to do: Mention to the doctor or nurse that what you're seeing is a sudden change for this individual, because, often, medical staff (who don't know the person as well as you) think such symptoms are "just the dementia."