I don't feel right. like i'm about to die or have a cardiac arrest is it possible to know that or is this anxiety?

Panic attacks?: Lots of possibilities, but you need to see a good psychologist. You may be having panic attacks, which properly trained psychologists can successfully treat in a few sessions 90% of the time. You're taking celexa, (citalopram) which suggests you may be depressed. In any case, get thee to a good psychologist. Don't suffer for nothing.

Reassurance: It is hard to be so complacent. The best way is to present to you doctor when you are having the problem and he/she can do at least an ekg and interview you better. Reassurance always have to have a basis and the basis is when the right things have been done, only then you can sit down with the doctor, be reassured so it happens again, you know what to do.