Say you are a person of faith, you fear death, but believe that when you die you will be re-united with your loved ones who've died before you.

Then somehow you die, and there's nothing, no relatives, no golden gates/tree of life/any of those religious images. You are all alone in the blackness.

If somehow you were brought back from the dead, think about this:

Would you fear death more, or less than you did before?

You fear the unknown.

Now that you know, you don't fear. That doesn't mean it's a pleasant experience.