Psychosis is an abnormal condition of the mind that involves a loss of contact with reality. People experiencing psychosis may exhibit personality changes and thought disorder. Depending on its severity, this may be accompanied by unusual or bizarre behavior, as well as difficulty with social interaction and impairment in carrying out daily life activities. Psychosis as a sign of a psychiatric disorder is a diagnosis of exclusion. That is, a new-onset episode of psychosis is not considered a symptom of a psychiatric disorder until other relevant and known causes of psychosis are properly excluded. Medical and biological laboratory tests should exclude central nervous system diseases and injuries, diseases and injuries of other organs, psychoactive substances, and toxins as causes of symptoms of psychosis before any psychiatric illness can be diagnosed. In medical training, psychosis as a sign of illness is often compared to fever since both can have multiple causes that are not readily apparent.