(Formerly called manic-depressive illness) Characterized by the occurrence of mania (euphoria) alternating with bouts of depression. Bipolar disorder is characterized by changes from one extreme mood to its polar opposite -- for instance, from depression to the euphoric or grandiose state known as mania. The mood disturbances can be so severe that the individual loses touch with reality. He or she may feel suicidal when depressed, and when manic may engage in risky or self-destructive behavior such as spending large amounts of money, gambling compulsively, etc.