Rapid cycling bipolar disorder is a mood disorder in which a person has four or more episodes of manic behavior or depression with a year. It's called "rapid cycling" because the person can have severe, drastic mood swings over a period of a few days, or even hours. These changes in behavior can be disabling. It may seem like the person is "out of control." Follow the links below to find WebMD's comprehensive coverage about rapid cycling bipolar disorder, what the symptoms are, how to treat it, and much more.