Hi John,
I am sorry you are struggling so. I just want to say though, that it is totally normal for you to be afraid of dying and have fear/anxiety around it. Don't think that there is something odd with you for feeling that way. Even Jesus was very anxious/upset before going through the cross, and He knew exactly what was on the other side. Its very normal, heck this life here is all we currently have experience with.
I know I've been struggling some with this too since my husband had some pretty rough medical issues this past year. Its tough.
*Hugs* You are a Christian, and you have been saved, so you are going to the right place. I know its real tough to have just head knowledge and still feel afraid anyways. I get this too. Like I know I'm going to go to heaven, but it scares me too just like you, the whole how/what/when of it. I think most people when you get down to it, would admit to being afraid too, perfectly normal.
Prayers for you that you gain some peace on this, and that God helps you not feel so afraid. Hang in there, no matter what it *will* end up okay.