Great yoga, bad knee

I can't believe I hurt my knee tonight.  Normally, my knee will get sore during yoga, or other activity, but tonight I think I really hurt it.  I was trying to keep my leg straight during a hamstring stretch, and I think I hyperextended it.  I haven't been able to fully straighten it all night.  I am hoping that if I take an ibuprofen and go to bed early, it will heal overnight.  I'm not sure if it's possible, but I am hopeful.  Cross your fingers for me?