We have no data on the experiences of people who don't come back so it's complete speculation. We do have data on coma dreams; a quick check shows that they are compatible with NDE evidence, although some comas leave permanent neural damage and few reported NDEs do, despite their short-term lethality.

Some have speculated that the physical death process informs neuronic overstimulus that explains NDEs, and my point is that many aspects of NDEs don't fit that at all. Many skeptical of NDEs were confronted by the evidence of their own, or their patients', experience and could not gainsay its inexplicability.