psychosis

n. 1. An abnormal mental state in which a person's cognition is sufficiently disturbed so as to be unable to perceive reality in a normal manner so that he/she has either hallucinations or bizarre delusions which he/she thinks are real as well as disturbances in affect. Disorders usually considered forms of psychosis include schizophrenia, schizophreniform disorder, schizoaffective disorder, delusional disorder, brief psychotic disorder, folie à deux, dementia, and druginduced psychotic disorder. 2. In older usage any mental disorder that grossly disturbs everyday functioning.