What mental health disorder is characterized by alternating periods of depression and mania?

Bipolar disorder is characterized by alternating periods of depression and mania. Individuals with this condition experience significant mood swings that can range from depressive episodes, which include feelings of sadness, hopelessness, and a lack of energy, to manic episodes, where they may feel euphoric, excessively energetic, and engage in risky behaviors. These mood changes can profoundly affect daily functioning, relationships, and overall well-being.

In contrast, major depressive disorder is marked solely by persistent feelings of sadness and loss of interest, without the manic episodes that define bipolar disorder. Generalized anxiety disorder involves excessive worry across various aspects of life but does not encompass the mood fluctuations seen in bipolar disorder. Borderline personality disorder includes emotional instability and impulsivity but is not characterized by the distinct episodes of mania that occur in bipolar disorder. Thus, the defining feature of bipolar disorder is the cycle of mood disturbances, making it the correct choice in this context.