These are just two of the books that I often recommend for those of us who suffer health worries and anxiety.
http://www.amazon.com/Overcoming-Health-Anxiety-David-Veale/dp/1845298241
http://www.goodreads.com/book/show/9684360-overcoming-health-anxiety
Even if you have no intention of buying them...I just want you to click the links and have a look at them. I want you to see that there were actually people who had to write these books. Why? Because there are many, many people like you and me who have (had) this issue!
You are not going to die...you are not sick...you have a fairly common anxiety issue that happens to focus on being sick and dying.
There is a world of difference though! I know that it is still scary...that you still believe that you are not okay...but I am telling you that you are indeed fine...just dealing with extreme fears.
The fact that these books exist, further enforces what I am saying to you.:)
Try to trust in this for now. Keep working on your issues. It will get better...I am proof.
S.C.