What characterizes bipolar depression as a mood disorder?

Bipolar depression is characterized by mood swings that include both depressive episodes and manic or hypomanic episodes. The term "manic-depressive behavior" reflects this dual nature, highlighting that individuals with bipolar disorder experience periods of elevated mood, energy, and activity levels (mania) as well as episodes of depression. This distinction is vital for understanding the bipolar spectrum, as the fluctuations between these states are central to the diagnosis and management of the disorder.

In contrast, chronic sadness, severe anxiety, and social withdrawal can occur in various mood disorders but do not specifically define the presence of both manic and depressive episodes, which is unique to bipolar depression. This fluctuation between the high and low moods differentiates it from unipolar depression, where only depressive states are present. Hence, the identification of "manic-depressive behavior" encapsulates the key characteristic that helps differentiate bipolar disorder from other mood disorders.