What Causes Severe Knee Pain After An Adventure Trip?

I was just recently on a trip in Costa Rica and towards the end of the trip I started to feel a weird pain and sensation in the back of my knee, it feels like something wants to come out of the back of my knee. I started to get this weird sensation after I went water rafting and had to keep my leg hooked under something to stop me falling out of the raft. Once I got back, I was playing guitar hero on the drums and when I stood up i felt this stabbing pain on the opposite leg in which i was not pedalling with. I was limping for about 2 hours then the pain ceased. It was in the same leg that I had the other feeling on the trip I was on. Maybe theres a connection? Can you please tell me what might be wrong? Thanks Tommy