Always wondered if the likes of DMT or trace amounts of it contribute to these experiences similar to how adrenaline is produced during fight/flight response.

Could it be possible that the brain sensing no more blood is being supplied then triggers a mechanism to release this chemical (and in what quantities)? Wildly speculating as a layman, however, maybe there is a link between dream states / DMT production/synthesis and these experiences which are yet to be explored further.