Bipolar disorder is a cyclical mental illness characterized by extreme fluctuations in mood, energy, and behavior. It involves periods of mania, where a person feels abnormally elevated or irritable, and periods of depression. The causes are believed to involve genetic and environmental factors, as well as imbalances in neurotransmitters like serotonin and dopamine in the brain. Diagnosis involves using rating scales and diagnostic criteria from manuals like the DSM-5. Treatment options include mood stabilizing medications like lithium, antipsychotics, and antidepressants under psychiatric supervision. Lifestyle changes and psychotherapy can also help manage symptoms.