What might be happening in human beings who experience near death is that they are getting cold, but before they get so cold that they would die, they're actually diminishing their oxygen consumption in a way that is unknown. And that extends their survival limits, so they can appear dead but actually not be dead.
What do I mean when I say 'suspended animation'? It is the process by which animals de-animate, appear dead and then can wake up again without being harmed. OK, so here is the sort of big idea: If you look out at nature, you find that as you tend to see suspended animation, you tend to see immortality.