Unfortunately it can be. But the good news is that if you communicate your concerns and fears most dentists are sensitive and will go slow and give you as much Novocain as needed. I have had both pleasant and not-so-pleasant experiences. It also really depends on how bad the tooth is. If it is abscessed(not sure if that term is correct) the dentist should have you on an antibiotic a few days prior to the root canal. If possible try to schedule the procedure with an endodontist because that is their specialty. Many offices also offer sedation dentistry. I hope this helps. Good Luck and Don't worry.