Did I sprain my knee or strain it or something?

Ok today at school I was running down the hallway and I tripped over my friends leg while she was bending down getting something off the floor and I fell and hit my knee on the wall really bad. It took me a couple minutes before I could get up and I sat down. When I had to get up, I felt this sharp pain in my knee everytime I take steps. The sharp pain is right underneath the patella (knee cap). My knee also "wobble" like there is no bone and I keep almost falling cuz of my knee "wobbling." Did I sprain it or something? This is the first time I ever hurt myself this bad and I never had a sprain or broken bone before.