It is a type of long-term (chronic) mood disorder characterised by a persistently low mood most of the time, with the patient experiencing a constant sense of inadequacy, a loss of pleasure and an inability to enjoy life.
The need for food, drink and sleep may diminish, but it is the low mood that is most affected; the person affected feels a sense of confusion about life and a distress they cannot describe. It usually begins gradually, but once it starts, it often persists.