So I was riding back home today. As I was riding along I noticed shifting into a higher gear for my rear derailluer was getting harder and harder (stiffer to move lever). By the time I got near home the lever had completely seized up and only would go in a fraction of as far as its suppossed to. Now it wont go in far enough to shift gears at all. Any ideas on whats wrong?

Also all the other functions work for the front derailluer and shifting into lower gears.