OP I had all the symptoms you have. I had a lot of CBT when it got to the stage that I thought I was having a heart attack when going up the stairs and I was in constant fear.
I didn't believe that it was anxiety either. I didn't believe my heartburn, gas, palpitations, feeling like something was stuck down my throat and so on were anything other than a serious health problem that was going to kill me. I got help for my anxiety and I am so much better. I still get mild anxiety over this . I take a propranolol and I soon calm down now, but I also have my CBT skills to help.
I get palpitations when I have heartburn, I get heartburn when I am anxious, I then panic and get worse heartburn. I can end the cycle quite well now but in the past I was just like you. There is nothing you have said that I don't relate to.
I could have wrote your post a few years ago, and in fact I did elsewhere. It is very hard to accept that it is anxiety in the first place, I understand that, but you have been giving the all clear, you have been told it is anxiety and people here have had the same or similar experiences.
My anxiety used to tell me that if I accepted it was anxiety and I did actually die it would be my fault. I felt like I was somehow in control when I was worrying and in some strange way keeping myself alive. Just the anxiety talking and I had to fight that bastard hard.
Please get proper help for your anxiety, you really don't have to live like this 