Imo this is the worst manifestation of Anxiety as you can't run away from it. It's been a huge problem for me since I was a child.

Meds help. I'd rather take medication for the rest of my life than live in the hell of death anxiety. It makes me physically I'll for months and makes life lose all value, 'it doesn't matter if my life is amazing or horrible if it's all erased in the end'. I wish I could be spiritual but nothing genuinely convinces me in religion or pychics etc. Please go to a doctor, while the fear is normal and human, obsessive death fears means there's something wrong (brain chemistry/mental health wise)

When I'm doing OK my thought process is this: we have no idea what the hell goes on with life and death, everyone only has theories, I should not obsess over the one I find scariest. No matter what happens, I will always exist, in my time. Kind of like if you walk alongside a long painting, the parts you've walked past don't disappear just because they are behind you, they exist in their part of the painting. I won't cease to exist, I'll always exist in this universe between the date I was born till when I die.