I dislike dental procedures. I especially dislike it when the drill whines its way through another bundle of nerves, the sucky thing does an excellent job at pinching a chunk of lip between itself and the tooth it's hooked over but fails to remove all the saliva and debris, and the throat is trying desperately not to swallow all the muck that forms at the gateway to the uvula, which results in a kind of gag reflex.
At such moments, now and then, I tend to try and force myself to relax (I've done a stress course, y'know) and become aware of how tightly my hands are clenching the armrests.
During all of this there is some soothing daytime soap or kids program on the led tv screen mounted on the ceiling.
Nitrous was the panacea. For the more involved procedures (ie likely to be prolonged and/or painful), it was my go-to.
When my dentist stopped supplying it, the alternative was tranquilizers. Temazepam, 15mg, makes the whole thing a relaxing experience. Takes the edge off very nicely, thank you. No gag reflex, (or if there is, it doesn't bother me), no white knuckles, and any pain that breaks through the lidocaine block is met with a sort of academic mental curiosity, rather than dread.
You could get your doctor to prescribe you some. Will also help with sleep on a long haul flight. Should not be mixed with alcohol. I find two glasses of wine after the meal seems to complement the action rather well, regarding a sleep aid.
(Or you could just try alcohol on its own. It can be a pretty good tranqulizer.)
I've also been prescribed diazepam (ok), and some nasty crap called hypnoval. (That's the one they give you before surgery, so that if you wake up, you're less likely to remember it.)
Hypnoval left me feeling like a chunk of my memory and brain function did a midnight creep. Took over two weeks to get back to normal.