Take it from a reformed Panic Attack sufferer, who is a hypochondriac as well. Here's the deal -
While your chest pains certainly are cause for concern, through my cognitive behavioral therapy, I have learned that it boils down to one simple question for me:
"Have I had this before, and how did I do back then?"
The problem I had is a heightened awareness of everything happening in my body. Equate it to a noisy refrigerator. There is always some kind of noise going on, but it still works fine. The problem with being hyper vigilant is that you NEVER get a break.
Take a student - they study for hours on end, then they need to take a break, or they are too tired. Same goes for someone at work. When you are hyper vigilant, you NEVER take a break, so you are exhasted, which further fuels the anxiety and symptoms. It's a viscious cycle.
Take all the times you have had the bad things happen to you (in your mind,) and look at them as proof that you "survived" despite your thoughts to the contrary. Each time you had an EKG, (and I have had over 12 in the last year. LOL) each time you visited the doctor, each time you suffered are actually proof that you are allowed to be okay.
Finally, I had to ask myself, what does being hyper vigilant give me? When I am constantly checking, or waiting for something bad to happen, what is that giving me?
The truth is, if something's wrong with your heart, (in the case of a medical emergency,) NO AMOUNT OF VIGILANCE is going to help you. There will be NO QUESTION as to what's wrong. At your age, it's rare. (You have a better chance of winning the lottery!) You would have to have something wrong already, like a bad heart defect, which has been ruled out by your doctors.
Finally, I knopw it's hard, but try and get off the anxiety meds. They are fueling your anxiety, and are a crutch. Your road to recovery will have many setbacks, (mine did,) but in the overal picture, it will go down.
If you need any more help, don't be afraid to look into CBT. If it's really expensive for you, (a session around here costs 110$, and you are looking at minimum of 10 session!) you can try a university where they are training their students under supervision of a psychologist. I paid 20$ per session then, and my insurance picked up the tab for most of it.
Good luck, hollar if you need anything!