That's nothing! You should see the bruises I get at work every day! My thighs are covered with them, and I worried for a while that they would never heal because every other day I would go to work and re-injure myself. They're doing a little better now, thank goodness! Maybe you should ice your knees just in case there's some delayed swelling or something. Or soak in a hot bath. I think that helps me, but it's hard to tell, with a bruise.