In an NDE, we are asked to believe that the person having it is actually experiencing reality- but Paul did not know, when he was caught up to the third heaven, whether he was in the body or out of it- and Paul was an experienced traveler in the spirit, having been raised from the dead(or near death) after stoning, raising a man from the dead, etc.
I do not believe all NDE's are invalid- I just believe they are interpreted according to the religious misinformation of the people that have them. I also believe some of them ARE invalid/phony/demonic/etc- especially the ones that end up in million selling books where the person gets rich off it :o)
A person sees the spiritual reality of Gehenna or the lake of fire, but they are not yet able to process it because they are carnal, because they are in a vision, and, because it is still a terrible thing to fall into the hands of the living God. The vision of His wrath is, for the natural mind, perhaps a very difficult pill to swallow.