hey, i know what your going through
im/was very similar to you, when i was young i use to cry myself to sleep cus i feared death that much, and i brought along one of my first anxiety problems
if im correct its not that you are scared of dying physically but more of scared about whats after death
me for example i use to think well when im dead, im dead, thats it, one day i wont be here, game over type of thing, but i wasnt scared of how i was going to die
i use to fear my parents dying, it use to freak me out that one day i will never see them again
whenever i would think of any of this stuff, i would snap out and shiver and fell as tho i just wanted to run

i will tell you know i am 95% better, i have the odd occasion now and then when it happens but 5/10 mins after i 4get about it
i dont know how old you are but what really helped me was saying its ages away, i have soo much to look forward to like driving, getting marrid, having kids and so on

so yeah i pretty much just grew out of it
so dont worry it will pass