I have never had one but I do know quite a bit about them (I am currently applying to dental school and have shadowed with a root canal specialist). They usually aren't painful (its the dentist's job to make it comforable) but sometimes people are hard to get num...thats just the way it is.
If you are really terrified about it there is some things they can do. If you have someone to take care of you (so take you to the dentist and home and stay for a little bit) I would ask if they are willing to perscribe Halcion (Halcion is the trademark name, the drugs real name is Triazolam). This drug is a sedative and it works very well. You will have to go to the dentist and get a perscription and fill it so you can take the pill before you have the root canal. They will probably only give you 1 pill, they are very small but VERY effective. You basically will not know whats going on and you will remember very little. Better yet, it is inexpensive ($3-$5 per pill probably).
I am not a doctor (yet) but I have seen this pill used for this purpose and it works wonders so if you are really worried I would ask about it...it couldn't hurt. Of course, sometimes there are special circumstances that medications can't be used...but again, it never hurts to simply ask.
