I know exactly how you are feeling about
being anxious about
the rapid heart beats. I have had those for years. I have experienced palpitations also. I have had a mirage of tests that have all come back fine. I even had an mri of my heart last year and at times I still think there's something the doctors are missing.
As long as you have had the tests that the doctors feel you need with your symtoms and they are all fine, then the next step is to just relax when these problems come up. You can either do that by deep breathing and relaxing or for me I need to just get my mind somewhere else. I play solitary or go on the computer and look for travel ideas even though you might not be traveling soon but get your mind on other things.