Bipolar disorder, also known as manic-depressive illness, is a brain disorder that causes unusual shifts in mood, energy, activity levels, and the ability to carry out day-to-day tasks. There are four basic types of bipolar disorder; all of them involve clear changes in mood, energy, and activity levels. These moods range from periods of extremely “up,” elated, and energized behavior (known as manic episodes) to very sad, “down,” or hopeless periods (known as depressive episodes). Less severe manic periods are known as hypo manic episodes.