What could be wrong with my knee?

Last night I couldn't see where I was going and ran into a bedpost. My knee didn't hurt much at the time, but when I got up this morning if anything touches it it is excruciating pain and it is messing up my walking. I have bruised that kneecap a couple years ago so I am wondering if I could have bruised it last night. Does anyone know what this could be if it does not sound like a bruised bone?