I can relate in a big way. I've had an ongoing heart attack feeling for 20 months. You name the heart symptom, I've probably had it, and 20 months of feeling like you're going to die any second is just too much to take. I've had 3 or 4 EKG's, 3 or 4 blood draws looking for cardiac enzymes. I've worn a 30 day event monitor, nothing ever comes back bad (which is great!). I've also had 3 MRI's of my spine and a couple CT scans, along with other tests that never turn up any reason why I'm suffering.
So I'm left with horrible, debilitating pain. I've gone to physical therapy (30 times) and chiropractic (about 15 times), which has been the only thing keeping me out of the loony bin trying to cope with pain. My pain will wrap around from the front of my chest to a spot on my spine. I use a hard foam roller at home to keep my vertebrae loose and moving. It will hurt when they lock up, which makes them lock up even more, and hurt more, like a downward spiral of insanity. Today has been particularly bad, but I'm plugging along. So, I can totally relate.
What to do from here? Try doing what I do. I try to focus on the fact that 1. I'm not dead after twenty months of a heart attack. 2. I've had so many tests, I'm way better off than the average person walking around with no idea of their heart-health, which leads me to point 3. Believe the tests!! As someone that struggles with HA, you need to believe the tests. No test will ever give you the peace you seek if you constantly get into a cycle of "what if they missed something." Believe me, I know as well as anyone that pain can really mess with your mind, and it's hard to do. But it can be done.