Yes and No. You probably had you mouth open for quite a while and your muscle is sore. Your gum may be irritated from the clamp. The disinfectant used to clean the root canal can irritate as well. If you don't feel better after 2 days call your doctor (or sooner if you're concerned). Meanwhile, take whatever you dentist prescribed or Ibuprofen 600mg every 6 hours. You should not be in extreme pain, howeve.
It Can Happen. The majority of patients find discomfort following a root canal or retreatment to be mild. Sometimes there can be post-op pain that is more severe, and those cases usually occur with retreatments. It is believed to be due to an exaggerated immune response to the bacteria or infected debris within the canal. It usually resolves by itself but sometimes requires medication or a follow-up visit.