DH is a dentist & I've worked in his office for several years now. The best advice that I can give is that if you are having lots of pain and swelling in the area now, have your dentist put you on an antibiotic before you go in for the procedure. This helps decrease the infection in the area and alleviate the pain after the procedure. If the anesthetic is properly used & the infection is under control, the root canal itself should not hurt. The pain afterwards comes partly from the drainage of the canal into the surrounding tissue. Starting on an antibiotic for a couple of days before your appointment helps minimize any pain later. You'll be fine - my dh is a general dentist and does endodontics all the time, for which he was fully trained in dental school. He has all the appropriate equipment & keeps current on new materials and techniques through continuing education. He refers special or difficult cases to the endodontist. If you are especially nervouse you might ask about nitrous oxide. (Laughing gas)
You are making a wise choice to do this for yourself and save the tooth.