Bipolar disorder is a mood disorder that alternates between high mood and low mood. When the mood is high, it is called the manic phase or light manic phase; when the mood is depressed, it is called the depressive phase, so the disease is called bipolar disorder. And bipolar depression refers to patients diagnosed with bipolar disorder who are currently in a depressive phase. Bipolar depression is very similar to depression during depressive episodes, but are two very different disorders with different treatment options, and need to be carefully identified.