delusional

Suffering from delusions; having false or faulty beliefs.

You're delusional if you think that plan will work.

Morgan could not remember the last time he had heard his first name used, and he had not even been aware that Captain Jackson knew it. Regardless, he could not reply; he was sure he must be delusional. He had lost too much blood […]

Being, in the form of, or relating to, a delusion.

Delusional jealousy […] A delusional belief that one's partner is being unfaithful. This can occur as part of a wider psychotic illness, secondary to organic brain damage (e.g. following the 'punch drunk syndrome' in boxers), […]

The latest act in the Madness of King Donald drama playing globally on every channel underlined the increasingly delusional world the anti-hero inhabits, his fantasies fed and indulged by a cast of sycophants, lackeys and straight grifters, all in it for what they can get.

A person suffering from a delusion.

But of course, that excludes the narcissistic delusionals, the deliberate frauds, and the pathological cases of multiple personality. They are all out there in New Age Land, and it's a jungle!