How is bipolar disorder different from major depression?

Lability: Bipolar disorder has discrete periods of depression in addition to discrete periods of feeling "too good".

Bipolarvs Depression: Actually, according to the criteria used, one may have only ever had manic moods, or mania, and qualify for the diagnosis of bipolar disorder. That is why the term manic-depression is confusing. One may never have been depressed at any time, and still have bipolar disorder.

Mania: By definition, in bipolar disorder th person must have had one episode of mania or mixed presentation.