Docs can you explain what is a bipolar disease and is it a rare disease?

Bipolar: Manic depression is a mood disorder that presents with extreme highs & lows, with at least few weeks of manic phases (abnormally elevated mood & energy level) alternating with few or more weeks of depressed phases (sad, guilty, hopeless/helpless, changes in sleep/appetite/energy level). Any phase can be severe enough to experience delusions or hallucinations.