By coincidence, I have this appointment that I have been dreading with the dentist, tomorrow 20/5 (I mean for root canal treatment, whether they use any general anaesthatic, I have no idea but I've asked in the past)
TBH, your discomfort is understandable but a very good one which I would have loved to share.
Somethings are better left unsaid but the thoughts and imaginations of what w/could be, can be so unsettling. That said, mine doesn't compare to what you are handling. Maybe mental toughness would help!