Bipolar disorder is a serious mental illness characterized by extreme mood swings from depression to mania. These moods swings are called episodes and include depression, mania, hypomania, and mixed moods. Treatment involves medication, therapy, lifestyle changes, and social support. Bipolar disorder has no single cause but is believed to involve genetics and environmental and psychological factors. Sylvia Plath suffered from bipolar disorder and described her experience with it in her book The Bell Jar.