Bipolar disorder, also known as manic-depression, is a mental illness characterized by wide mood swings from mania (euphoric/irritable states) to depression (hopeless, unhappy states). A person with bipolar disorder usually returns to a normal mood in between episodes of mania and/or depression.

Some people with bipolar disorder experience something known as a mixed episode. People in mixed states alternate between mania and depression on a daily basis for at least a week. Roughly, a third of people with bipolar disorder experience at least one mixed episode during the course of their illness.

Cyclothymia is similar to bipolar disorder since it involves fluctuations between depression and mania.

It is often times treated with mood stabilizers.

Examples:
Depakote (valproic acid)
Tegretol (arbamazepine)
Lithium
Dilantin (phenytoin)