Originally Posted by Xurtio

Dementia is a disorder, but informal usage of "demented" simply implies irrationality. Everybody is capable of demented thought, even if they are subclinical.

As another example, someone experiencing anxiety does not necessarily have an anxiety disorder. For the trait to be considered a disorder, certain criteria have to be met (there are three criteria in Alaska clinical practice). I'm aware that diagnoses can't actually be given out over the internet.