I might be able to help. I have had a fear of a heart attack since my very first attack. Long and short of me is a family history of heart disease, I'm a smoker, I used to drink and I worked out alot. I had my episode on a tread mill and a few after over the course a a few weeks. My heart is A-ok and there is nothing physically wrong with me. I've been in CBT for a while and I'm on low dose zoloft. Ok, my credentials are out of the way.
I have had those fears of death as well. First have you seen a doctor for a check-up/diagnosis of A/P? This is a symptom of it in some people.
Also, one thing that works for me is accepting the things in this life that I can control to live longer. Eating healthy, eventually going back to the gym, quitting smoking, etc. Taking charge of what you can control in reguards to your health can give you a positive attitude about life which in turn might sway some of the fear of death.
This is the hard part, also accepting that if you do die, that it is going to be, irreguardless of what you do about it. Some people get tagged by a car while they sit in there living room. I'm not trying to scare you but somethings in this life we cannot control. Are you afraid of death, or not having control over life?
I'm not a doctor/health proffesional. I don't know anything about you/ your history, etc. If you feel you need it seek a doctors advice. Find help with your family and friends and church. I know these ideas I put here aren't answers but they should hopefully get you started in the right direction.