First of all, there is no need to panic, because I'm basically doin' aiight.
But, if you go to the emergency room, know two things.
One. That's basically your day. Bring a good book for the waiting room. Try not to freak when your in the exam room for extended periods by yourself.
Two. If you don't have chest pains, be real clear on that fact. If you're all, "well, maybe" they won't leave you alone on it.