Back to the 1994 Lempert article about syncope and NDEs that's one of the cruxes of this article, I see Bruce Greyson did respond to it in the "altered blood gas levels" section of his chapter on explanatory models of the NDE in
T:he Handbook of Near-Death Experiences:
One of the earliest physiological theories proposed for NDEs is that lowered levels of oxygen - hypoxia or anoxia - have produced hallucinations (Blackmore 1993; Lempert 1994; Rodin 1980). However, NDEs occur without anoxia or hypoxia, as in non-life-threatening illnesses, falls, or other near-accidents. Furthermore, the experiential phenomena associated with hypoxia are only superficially similar to NDEs. James Whinnery (1997), who compared NDEs to what he called "dreamlets" occurring in brief periods of unconsciousness induced in fighter pilots by rapid acceleration, argued that some features common to NDEs are also found in these hypoxic episodes, including tunnel vision, bright lights, brief fragmented visual images, a sense of floating, pleasurable sensations, and, rarely, a sense of leaving the body. The primary features of acceleration-induced hypoxia, however, are rhythmic jerking of the limbs, compromised memory for events just prior to the onset of unconsciousness, tingling in extremities and around the mouth, confusion and disorientation upon awakening, and paralysis (Whinnery 1997), symptoms that do not occur in NDEs. Moreover, contrary to NDEs, the visual images Whinnery reported frequently included living people, but never dead people, and no life review or accurate out-of-body perceptions have been reported in acceleration-induced loss of consciousness.
Greyson, Bruce. (2009) "Explanatory Models for Near-Death Experiences". In
The Handbook of Near-Death Experiences (p. 217). Santa Barbara, CA: ABC-CLIO.