Thats exactly how I feel everytime I go to the dentist - Like a lamb to the slaugter. I hope it goes well for you, and you experience no spike from it.
So spot on @SugarMagnolia. Have you been taking NAC, magnesium and others in preparation? It might be ok that they just need to clean a bit and redo the filling without too much drilling. Let them know about your T and for them to take it EZ.