That's why chocolate helps, why they generate feelings of hopelessness, why they take away happy memories and leave unhappy ones, and why their ultimate power is to put people into a coma rather than to kill them. None of this makes sense for a manifestation of death.

I don't know about chocolate, but bad memories are definitely scars you get from death. And what I suspect triggered the idea in Eliezer's mind to make Dementors be about death is the idea of the Dementor's kiss, because of the old metaphor "kiss of death".