This group includes disorders in which episodes of mania (periods of excessive excitement, activity, and energy) alternate with periods of depression. Bipolar disorder is characterized by shifts in mood as well as changes in activity and energy levels. The disorder often involves experiencing shifts between elevated moods and periods of depression. Such elevated moods can be pronounced and are referred to either as mania or hypomania. Mania is characterized by a distinct period of elevated, expansive, or irritable mood accompanied by increased activity and energy. Periods of mania are sometimes marked by feelings of distraction, irritability, and excessive confidence.