Can myofacial tooth pain/throbbing post root canal show up elsewhere? Scarey to have more dental work done now. Will it happen again?

Sometimes. Is not normal to have that kind of pain after a root canal, don't be discourage to continue your dental treatment.
Post rct pain else. Not likely most likely coincidental that the pain showed up elsewhere.
Not usually. Usually post rct pain lasts about 3-5 days. If there is still severe pain then other teeth need to be examined. Post op pain from root canals does not spread to other teeth or areas of the mouth. However, people can react differently to dental treatment. Each case has to be handled according to how the individual patient reacts to the treatment.
Uncertain. I am not familiar with the term myofascial tooth pain. The pain you have post root canal needs to be clarified by your dentist. Is it only in your mouth? Myofacial pain is usually in the soft tissues not the mouth but elsewhere in the body. Sometimes after dental work one can have temporomandibular joint pain? This is pain in the jaw joints. Is this where you have your pain?
Myofascial. Myofascial pain is muscle pain. Not the type you woiuld normally see after a root canal. Best bet see the dentist who did root canal. Should not happen again due soley to dental work.