Actually, the NDE site i posted supports this part of your statement. There are examples of NDEs from people of various religions, as well as from athiests.
RE:"... which demonstrates that the NDE is of human, not supernatural origin."
Same site has a section discussing the skepticism of NDEs. I only looked at the titles of the articles, so don't know how detailed it is.
That NDEs cam be induced by altered brain chemistry, (or drug use), does not prove that all NDEs are only attributable to brain pharmacology.