"In the Tibetan-philosophy, Sylvia-Plath sense of the word, I know we're all dying. But you're not dying the way Chloe is."
I'm going to the doctor in a bit (hey, any reason to skip out on some class), so place your bets now. Closing in 15 minutes. Anyways, it feels a lot better after a night, still some pain when going up stairs, I haven't tried squatting but that probably would too. The winning bet gets my leg after it's cut off.
Since it seems to have ocurred suddenly, it sounds like some sort of cartiledge damage. You have similar symptoms to me, but mine doesn't hurt with just plain running. I have scarring on the articular cartiledge, and that is not good news if you have it. Best case is that you have tendonitis (like runners knee), but this usually has a gradual onset. Worst case is cartlidge or ligament damage which will need surgery. Good luck, go see a doctor and get an MRI.
Sounds like Patellar Tendonitis. But you should get it checked out either way. Until then, ice, ice, ice, ice and ice it. Icing it will shrinken the swollen nerves associated with the pain. Heating it is a no-no. (btw- I was a trainer fo 4 years, and at one time took pre-med for it, so I kinda get some of this stuff... a "psuedo-doctor" of sorts on sports related injuries.)
If you are going to an HMO, let me save you the co-pay. Rest. Take naproxen for two weeks and then come back if it still hurts. If you don't want to do that. Tell them you have done all that already. Seiously, stop doing what causes the pain for awhile. I assume you aren't on a tennis team or something.