For what it's worth, I have been extremely close to death a couple of times -- both times I was expected to die: when the horse kicked me in the gut when I was 21 and when an ovarian cyst ruptured, touching off my appendix, and I ended up with severe peritonitis when I was 30. Both times I spent time in extreme pain, floating in and out of consciousness. Neither time were their any lights or angels or anything else.
However, after the last, several days after the surgery, when I was still sinking and not expected to live more than about 24 hours more (from what I was told later), I knew I was dying. And it felt like sinking gently into a deep, velvety well where there was finally no more pain. I remember talking to my brother at one point on the phone and telling him I was just giving up. He got upset and I guess kicked a number of prayer chains into operation.
I obviously didn't die!
But that experience of sinking gently was peaceful. And, contrary to the ND experiences, there was no light, only a rather blessed and gentle darkness.
I would like to suggest that a number of visitations are the results of actual brain damage due to lack of oxygen during these times of death or near death, but that these brains also belong to people who had rejected Christ in the first place, and thus are subject to being manipulated by demonic forces. In other words, it might well be a combination of both the medical condition and the choices these people had made prior to the experience.
Edit: I think the two posts above mine do show that Christ-given experiences can happen as well, and I didn't mean to speak against that.