I am sorry you are dealing with these thoughts and fears...it is no way to LIVE, right?
I hope that you can discuss your concerns with your doctor tomorrow...and together come up with a good management plan for the anxiety that fuels these fears.
Here also are some book recommendations that I am posting for you because they both deal with health anxiety...and one of them has a chapter specifically regarding the fear of death. Don't forget also the health anxiety links for self help in the Resources. If you not checked them out so far, please do so!
Books for overcoming Health Anxiety:
Let us know how your appointment goes okay?
"Courage is not the abscence of fear, it is feeling afraid and doing it anyway!"
"Worrying does not empty tomorrow of its troubles...it empties today of its strength."
Corrie Ten Boom
Panic Syndrome recovery due to CBT