The extreme of bipolar disorder is depression. Depression is characterized by low mood, depressive thinking and physical or biological symptoms. Patients usually complain of low mood, frequent crying spells, lack of energy and loss of interest in daily activities. There is also lack of concentration in work and psychomotor retardation. Patients have pessimistic thinking about future and also have feelings of guilt, hopelessness and helplessness.
The physical symptoms include sleep disturbance, loss of weight and appetite, constipation, loss of libido and amenorrhea. Depressed patients also have frequent suicidal ideations and many even attempt suicide. In severe depression, psychotic symptoms like delusions and hallucinations may be present.
According to DSM-IV criteria, the diagnosis of bipolar disorder can be made after a single episode of mania lasting for at least a week, causing social and functional impairment and the symptoms are not caused by any medical condition or substance-induced disorder.
There is no single cause of bipolar disorders. It is an interplay of various factors including genetic factors, personality, predisposing and precipitating environmental causes and physical factors.