Well, from personal experience, I think that you are focusing on the event way too much and that has you in an anxiety loop . . . the same thing probably would have happened had you felt your heart was beating too loudly . . . once we trigger anxiety or anxiety triggers us, then everything just seems to go every which way . . .
So, my suggestions to you would be . . . if you are obsessing about a minor heart attack, go to your doctor, explain what happened, have him/her check you out . . . so you eliminate the focus of your immediate anxiety . . . . next, if you have not already done so, get yourself aligned with a therapist to help you with your hypochondria . . . you may need to check out a couple before you hit one that matches your needs . . . the good news is that at 21, your brain (anyone's brain) is not fully formed so now is the time for intervention . . . it is very frustrating and disturbing dealing with health anxiety because anxiety puts us in the loop and it is a hard one to break out of . . . .
Let us know how you are doing and know that if we can help, we will . . .take care, kc