why would a jw's brain show him visions of a kind of heaven when that image is not a part of my belief system?
That's some excellent reasoning! But I wouldn't stop my search for all revealed knowledge at the ending flyleaf of the Reasoning book, if I were you. ;-)
Look around, there's lots of info for and against the idea of near-death experiences having some sort of meaning.
Personally, I have had very vivid dreams in which I did things and saw things that I would never have imagined lurked in my brain. But they're there. It's not at all difficult for me to believe that near-death experiences are the result of your brain going off track for a bit.
If near-death experiences are real, it would mean there's something pseudo-random about going to heaven that sounds very un-god-like. Sort of a heavenly clerical error that I wouldn't expect from the almighty. But as has often been pointed out to me, god is not bound by my expectations.
Dave