It is also a clinical term used to describe forms of mental illness. When faced with stress such as loss of a loved one, relationship breakdown, great disappointment or frustration, most people will feel unhappy or sad. These are emotional reactions which are appropriate to the situation, and will last only a short time. It is not regarded as depression in a psychiatric sense, but a part of everyday experience. Because depression is so common, it is important to understand the difference between unhappiness and a depressive illness.
Schizophrenia is a serious mental illness which affects one person in a hundred.
The term covers a number of related disorders, all with overlapping symptoms. However, in all types of schizophrenia, the illness interferes with the mental functioning of a person and, in the long term, may cause changes to a person's personality. First onset is usually in adolescence or early adulthood. It can develop in older people, but is not nearly as common. Some people may experience only one or more brief episodes in their life.