I kneeeeed some advice?

I know a lot of you guys have had knee issues, so I figure I'd throw this one out there. I hyper extended my knee skiing today to the point that made this horrible sound.. kind of a mix of someone hocking up a bunch of flem and some jello hitting the floor, something like that. Anyway, its really sore right below the kneecap, I can still walk (limp) around and stuff, but for those who have had knee injuries: is it obvious if you've messed something up right away? I'm gonna give it a few days of taking it easy and decide then if I'll go to the doctor or not, but I don't know anything about knee injuries so I thought I'd ask.