Diagnosed as depressed about a decade ago. Never took my pills (all three batches, SSRI's and Tricyclics). Got a bit better, got a bit worse, got a bit better, got a lot worse.....
I think I'm bi-polar. My mood can go from absolutely joyous to stick-my-head-in-an-oven in a matter of minutes. Good times last days, bad times last weeks.
Not too worried though, I have less than a decade left according to my plan. The seemingly never-ending cycle has left me with a very morbid sense of humour, and an unhealthy disdain for my own life!
The main problem I have is that, if I do something awesome, like a bungie jump or some awesome airshow photography, I crash heavily the next day when things go back to normal. Everything just seems empty and pointless.
It's why I'm a biker. If you're gonna ride like a tit at 150mph+, held to the road by two credit-card sized pieces of rubber, it's best to accept that you're already dead!