Manic depression; Bipolar affective disorder
Bipolar disorder is a condition in which people go back and forth between periods of a very good or irritable mood and depression. The "mood swings" between mania and depression can be very quick.

There is more involved but basically it is "extreme" mood swings! In my case it is due to a chemical imbalance in my body and for me being on the right medications to help me control it!