It is not an illness perse, but rather a series of symptoms that may be associated with many diseases such as Huntington's disease.
People with dementia live in realities of their own.
Demented person: Hi, what's your name?
Me: Hi! I'm Ken. What's your name?
Demented person: I'm going to bed!
Demented person: Can I kiss you?
Me: :( //backs away nervously
1. Demented place, where everyone and the place itself is demented, madhouse.
2. Realm of the demented inside your mind, whenever you lose your mind your in dementia.