(Moving day, day two.)

I'm carrying a 70 - 80 pound box of my books when landing on one stair (descending) with most of my body weight, and now I can hardly bend my right leg at the knee. I don't know what I did but bending my right leg, even in the slightest, is now a chore. The one time I don't heed my father's advice about dividing weight when packing boxes for moving - this happens! GRRRRRR