A mood disorder is a mental health condition that causes intense mood swings, including shifts between manic and depressive states. When left untreated—because of the dramatic fluctuation between emotional states they cause—mood disorders can get in the way of day-to-day activities, responsibilities and relationships.
The National Institute of Mental Health reports that about 9.7 percent of U.S. adults suffer from a mood disorder in a given year, while an estimated 21.4 percent will experience a mood disorder at some point during their lifetime. Some of the more common mood disorders include depression, bipolar disorder and seasonal affective disorder.