It's commonly known as Manic Depression.
I was diagnosed with it in February 1996, after 3 years of absolute hell. This disorder is often misdiagnosed, as in my case.
The doctors had me on Prozac, Zoloft, Effexor and Lithium amongst other things I don't know the names of.
Currently I am not on any medication as I can't handle the side-effects, so I'm walking a tight-rope.
I can handle the depression better than the manic episodes. When I get manic I am totally out of control and I can do anything which really scares me. When I'm depressed I just eat alot (especially chocolate !!!!!) which generally makes me feel a bit better ... LUCKILY I HAVE A SUPER-DUPER METABOLISM !!!
Some great links :