I hurt my knee playing rugby yesterday - it felt like a hyperextension (my knee went very straight; almost backwards), and now I have some swelling. Not much pain, but it's swollen and stiff and not easy to bend. The good news is that it's stable, I can put all my weight on it, and walk fairly normally.

Any ideas? I'm hoping it's just a strain - I've torn my ACL before, and it was certainly more painful than this.