Bipolar disorder (previously known as manic depression) is a psychiatric diagnostic category describing a class of mood disorders in which the person experiences clinical depression and/or mania, hypomania, and/or mixed states. The disorder can cause great distress among those afflicted and those living with them. Left untreated, bipolar disorder can be a disabling condition, with a high risk of death through suicide.

The difference between bipolar disorder and unipolar disorder (also called major depression) is that bipolar disorder involves both elevated and depressive mood states. The duration and intensity of mood states varies widely among people with the illness. Fluctuating from one mood state to the next is called "cycling". Mood swings can cause impairment or improved functioning depending on their direction (up or down) and severity (mild to severe). There can be changes in one's energy level, sleep pattern, activity level, social rhythms and cognitive functioning. Some people may have difficulty functioning during these times