Bipolar disorder, also known as manic depression, is a mental illness that brings severe high and low moods and changes in sleep, energy, thinking, and behavior. People who have bipolar disorder can have periods in which they feel overly happy and energized and other periods of feeling very sad, hopeless, and sluggish. Hormonal problems: Hormonal imbalances might trigger or cause bipolar disorder. Environmental factors: Abuse, mental stress, a “significant loss,” or some other traumatic event may contribute to or trigger bipolar disorder.