Which of the following best describes Bipolar I Disorder?

Bipolar I Disorder is characterized by the occurrence of at least one manic episode or a mixed episode that includes symptoms of both mania and depression. This definition is critical as manic episodes are a key feature of the disorder. The manic episode is marked by an excessively elevated mood, increased energy, and often impaired functioning.

In addition to these key episodes, individuals may experience depressive episodes, but the defining characteristic of Bipolar I Disorder is the presence of the manic episode. Therefore, the option that best describes the disorder is the presence of one manic or mixed episode, as this captures the essence of the condition according to diagnostic criteria. Understanding this core feature is essential for proper identification and treatment of the disorder.