Bipolar I and bipolar II both involve shifts in mood, energy, and activity levels. However, they differ in the intensity of manic episodes and the prevalence of major depressive episodes. Bipolar I involves full episodes of mania, while people with bipolar II experience hypomania, which is less severe. Additionally, those with bipolar I may or may not experience a major depressive episode, while a major depressive episode is a diagnostic requirement for bipolar II.