Psychosis is a loss of contact with reality, typically including delusions (false ideas about what is taking place or who one is), hallucinations (seeing or hearing things which aren't there), and disorganized thinking.
Psychosis is associated with the manic phase of bipolar I disorder, schizophrenia, and schizoaffective disorder. Other conditions where psychosis may be present include postpartum psychosis, dementia, depressive episodes, Parkinson's disease and multiple sclerosis. The use of certain illegal drugs, including methamphetamine, can bring on psychotic episodes.
See also Health A-Z - Psychosis