I'll give you a piece of advice that's been very valuable to me, especially in the case of getting injections, which is always difficult for me. In the lead up to a local anaesthetic, and during, take a short-to-normal inhale through your nose (depending on your lung tolerance) and do a loooong, extended exhale, as long as you can extend it without needing to take too big a gulp afterwards. When you exhale, this pushes your diaphragm up into your heart, slowing your heart rate down and significantly decreasing the physical effects of anxiety.

It works very, very quickly, and if you do it for up to 5 minutes, the heartrate lowering effect can last several hours. Doing it regularly (5-10 minutes a day) has long term positive effects for your overall cardiovascular health, too.

I've never been one for meditation, but practices like that have probably been helpful to so many people because it naturally takes advantage of the relationship between breathing patterns and heart rate variability.

There are even more 'tricks' like this, such as the double inhale. Taking two very quick breaths in succession before that long exhale is even better at reducing your heart rate and generally calming you down. You've even done it before, but you wouldn't know it.

Children in particular will do this, and it can happen naturally when you're sobbing. Sometimes you'll take two short inhales like "huh, huh!" before going in for another cry rather than one big gasp- and this is why!

I hope this really helps you out, because it's very quick and straightforward, but boy does it work fast. Sometimes I've only remembered to-do it halfway through an unpleasant experience and it still banishes burgeoning pre-syncope and nausea. Good luck!