I have a 5 year old w/ ADHD and Tourette's who needs several teeth worked on. I'm also scared to death that he might have a problem w/ the anesthesia. I have been trying to hold off having the work done in the hopes that the teeth will fall out (the baby teeth usually start to fall out around 6 years old) before they cause any major problems. I have been brushing the decayed teeth several times a day w/ lots of toothpaste and watching for any signs of abcess (like a bump on the gum below the affected tooth). I'm not reccomending that you do this but I know the dilema that you are going through.
I do not have any experience in giving a patient sedation anesthesia. I teach with a dentist that does this and the chances of seizures i very small, but I certainly would discuss the possibility with the dentist that is doing the case.