It's happend to me also. In fact, I once had a tooth pulled without being numb because the dentist said he'd given me as many shots as he could without killing me. That was on the National Health Service, where they expect you to be tough. Over the years I've found that the local anesthetics made me feel unwell, though I'm not allergic, and so I now go without for all my crown work. I'd rather cope with the pain than with the rotten way the shot makes me feel - when I tell people, they always cringe.