The only advice I can think of, from someone who suffers a lot of anxiety for no apparent reason as well, is to try not to focus on that sort of stuff when it happens, because it'll compound on itself. For example if you have some kind of pain try to distract yourself with something like music or something that really takes your attention. I submerse myself in things that make me forget I even exist for a little while (a good show or a song) ... it's not really getting to the "root" of the matter but it helps me, and I'm sure it has to be some kind of good for your health. My anxiety led to digestive issues and those physical reactions get better when I immerse myself in something I'm passionate about.

I wish I could help more, that's all I got for you and myself at this time.