sle,
I also struggle with this sometimes. Here is what I found helpful
-Properly done diaphragmatic breathing. As someone mentioned, this helps to slow down the sympatethic nervous system (flight or fight responses) and trigger the parasympathetic system (which calms people down). Its one of the few ways to trigger that system. A lot of sites teach bad ways to do diaphragmatic breathing. The best one that I found is on drlam.com, he calls it ''Adrenal breathing'' but its the same principle. He also teaches a ''Adrenal yoga'' which I find even more powerful. Just a quick session of Adrenal yoga (and it does not resemble yoga in the traditional sense) and I can already feel a significant amount of relaxation through my body
-Meditation. Although, you might have already tried it. If you haven`t, you might try a typical meditation exercise found online for 1 month and see if it helps
-Improving self-esteem issues. Sometimes that reason the anxiety is being triggered has to do with undealt with self-esteem issues/childhood experiences. You might want to read The Six Pillars of Self-Esteem by Branden. That book saved my life 15 years ago
-Emotional freedom techniques, or EFT (the tapping sequences). Although this never worked for me, a lot of people report it working very well for them. Its quick and free to try so why not