What Is Bipolar I Disorder? Bipolar I disorder (pronounced "bipolar one" and also known as manic-depressive disorder or manic depression) is a form of mental illness. A person affected by bipolar I disorder has had at least one manic episode in their life. A manic episode is a period of abnormally elevated or irritable mood and high energy, accompanied by abnormal behavior that disrupts life. Most people with bipolar I disorder also suffer from episodes of depression. Often, there is a pattern of cycling between mania and depression. This is where the term "manic depression" comes from. In between episodes of mania and depression, many people with bipolar I disorder can live normal lives. What Are the Symptoms of Bipolar I Disorder? During a manic episode in someone with bipolar disorder, elevated mood can manifest itself as either euphoria (feeling "high") or as irritability. Abnormal behavior during manic episodes includes: Flying suddenly from one idea