I became demented overnight. Sudden onset is one factor that distinguishes my form of dementia from the more common form associated with Alzheimer's disease.

At 93, so deep in dementia that she didn't remember any details of her life, my mother somehow still knew songs.

In 1964, at the age of 39, Flannery O'Connor died from complications of lupus. She had lived with this autoimmune disease for 14 years, primarily confined to her mother's farm, Andalusia, in Milledgeville, Ga.

Dementia resembles delirium in the same way an ultra-marathon resembles a dash across the street. Same basic components, vastly different scale. If you've run delirium's course once or twice in your life, try to imagine a version that never ends.

Dementia is, after all, a symptom of organic brain damage. It is a condition, a disorder of the central nervous system, brought about in my case by a viral assault on brain tissue. When the assault wiped out certain intellectual processes, it also affected emotional processes.

Alzheimer's disease starts when a protein that should be folded up properly misfolds into a kind of demented origami.