drop foot

I don't know if I have drop foot or not. I never heard of it before I was telling someone at the gym I go to that since June I have been having trouble on the tread mill it seems my left foot starts to drag. Really weird as I've never had a problem before and I've been going t the gym for over 5 yrs. Can't understand what is happening. Could it be this drop foot. I don't have trouble walking or anything at a normasl pace.