The Facts
We all experience a variety of moods such as happiness, sadness, and anger. Unpleasant moods and changes in mood are normal reactions in everyday life, and we can often identify the events that caused our mood to change. However, when we experience changes in mood or extremes of mood that appear "out of the blue" and make it hard for us to function, these changes are often the result of a mood disorder.
Mood disorders are medical conditions that affect our ability to experience normal mood states, and there are mainly two types: major depressive disorder (also known as unipolar depression), in which all abnormal mood changes involve a lowering of mood, and bipolar disorders (formerly known as manic-depressive disorder), in which at least some of the mood changes involve abnormal elevation of mood.
Bipolar disorder typically begins for people during their mid-twenties. It is unusual for bipolar disorder to begin in childhood without strong familial risk factors and it is rare for its onset to occur after the age of sixty (unless associated with another medical condition). Bipolar disorder occurs in about 2% of the adult population.