Ok, first of all, you need to stop going to the ER. Even if you do have some sort of medical problem (which doesn't seem likely), the ER is not the best place to find that out, your regular doctor is. You should be seeing a doctor- make a real appointment, and stick with that one doctor. Think of it this way- if you do have a medical problem, who's going to know? Someone in a hurry and who only treats emergencies, or someone who knows your history and sits down with you on a regular basis? Not to mention it's a lot less expensive to see a regular family practice doctor.
Second, hypochondria is a form of anxiety. And that first episode you described sounds like it could have been a panic attack- the sudden feeling that you're going to die is usually a panic attack, along with the physical sensations.
So I would suggest seeing a family practice doctor. They could listen to all of your symptoms and would know if there was a medical problem that needed to be checked out, or refer you to a therapist of some sort to treat the anxiety problem. Either way, you need to someone and get help! You sound miserable!
danielle