Hello ladle: I don't know what the answer to your problem would be. I'm an older person & retired. So there's not a lot of stress in my life at this point. There still is some though. I think I lived with high levels of stress for so many years that my body no longer knows how to be otherwise. I do think that, if one lives with anxiety & stress long enough, over time, the "stress response" simply becomes a way of life, whether there's really anything to be stressed about or not.

You wrote you have tried breathing / relaxation exercises. I've done these sorts of things in the past as well. They tended to make me more anxious... not less. What I prefer is walking meditation. I walk slowly around-&-around our home front-to-back, slowly & quietly. I focus light-&-gentle attention on my feet as each one touches the floor. Thoughts come & thoughts go. I simply allow them to arise & fade at their own pace. I will sometimes walk for as much as an hour or two at a time. I also like to listen to quiet soothing music... a lot of it is various types of chant (Buddhist, Sikh, Hindu & other) but also the type of music that is typically referred to as "new age". There's lots of these sorts of things on YouTube. And I'm often listening to them when I'm replying to posts here on PC. I avoid engaging in things I know, before I start, would be arousing. From my perspective, it's a matter of coming to an understanding of what one can-&-can't tolerate & managing one's surroundings to encourage as much calmness as possible.