I was right. Depression is not necessary. Wikipedia:

Bipolar disorder or bipolar affective disorder (historically known as manic-depressive disorder) is a psychiatric diagnosis for a mood disorder in which people experience disruptive mood swings that encompass a frenzied state known as mania (or hypomania) and, usually, symptoms of depression.
Bipolar disorder is defined by the presence of one or more episodes of abnormally elevated energy levels, cognition, and mood with or without one or more depressive episodes.