Bipolar disorder was called manic depression when I was a kid. Basically, you have manic episodes (highs) where you think bizarrely, don't sleep much, spend too much money, and do stupid things. And then you have depressive episodes (lows) where you can't get out of bed and don't care if you live or die.
Anywwhere from 1-4% of the population has the problem. "The United States has the highest lifetime rate of bipolar disorder at 4.4%, and India the lowest, with 0.1%."The United States has the highest lifetime rate of bipolar disorder at 4.4%, and India the lowest, with 0.1%."
People are categorized into bipolar 1, bipolar 2, bipolar NOS, and bipolar 1 with schizophrenia. Usually. Bipolar 1 is like I described up above. Bipolar 2 has less high highs. Bipolar NOS means "not otherwise specified," and basically it's a catchall for all the other varieties of the probelm.