An interview on NDE's with a neurologist, from New Scientist. From this guy's research an NDE seems to be a merging of waking consciousness with REM consciousness. I found this interesting as during REM sleep, the brain produces PGO brain waves. These are also produced during an Iboga(ine) experience, which is interesting as the Bwiti state the you only encounter 'the beyond' twice during your life...during your initiation, and when you die.
www.newscientist.com

Near-death neurologist: Dreams on the border of life
Neurologist Kevin Nelson explains how the brain slips into a strange state of hybrid consciousness during a near-death experience