In a delusive or deluded manner.

A false belief that is resistant to confrontation with actual facts. / The state of being deluded or misled, or process of deluding somebody.

Producing delusions. / Delusional. / Inappropriate to reality; forming part of a delusion.

plural of delusion

The state or quality of being delusive.

The act of deluding oneself, or the state of being so deluded.

plural of delusion of grandeur

(usually in the plural) The false belief that one is important or powerful, accompanying certain mental disorders. / (usually in the plural) Conceitedness or overconfidence.

(psychiatry) A delusion in which the sufferer believes that a friend, spouse or family member has been replaced by an identical-looking impostor.

Cotard's syndrome.