Make sure you tell them that you took some meds before coming! And really try not to worry. I've had two root canals and neither were in teeth with cavities. They just feel off kind of. Like they're really sensitive, kind of like the tooth is out of place. The first root canal was on a tooth that I had a veneer put on and the work for the veneer disrupted the nerve. The root canal was almost painless. The only thing that hurts a little is the shot to deaden the nerve, and that just feels like someone is pinching you in your mouth. You will feel much better afterwards. Try to keep that in mind. And if it still hurts when they're starting to work, let them know! They'll take care of it.