Originally Posted by
IntoTheSunset
...
The next thing to do is to get the cable tension back where it belongs, and although I turned the barrel adjuster two quarter turns (one turn, test, another turn, test), my derailleur is grinding and struggling, so tomorrow it's into the shop.
I'm going to guess the problem is where the shift cable comes out of the shifter and goes into the cable housing that's attached to the handlebar. When your bike fell and the shifter got twisted, it jerked the cable sideways. Maybe kinked the cable, maybe just pulled the housing out of the little socket it's supposed to nest in. Should be an easy fix; possibly you'll want a new cable.
If the shifter was installed by a bike shop, note: it's the mechanic's fault. He didn't tighten the shifter enough.