Nonpareil said:
It isn't a particularly hard concept.
You know that philosophers are still discussing about 'what is reality?', 'what can we know?' etcetera.
So, it's not an easy question with an easy answer. There are many different concepts.
When someone had an NDE and he or she is telling us that:
-It's difficult to use words to tell about it ('using words to describe it' is all we have).
- It felt more real than our world here.
than we can discuss about the fact wich status we must give to such an experience or hallucination.
When different people, who do not know eachother, experience the same 'hallucination', then this hallucination has some status of 'being real'.
Some people argue that 'its because we are wired the same'. But that's not a strong argument. Because we don't have the same dreams, although we are wired the same.
Philosophers are still discussing and there is not one theory about 'what is real'?. So, it's not that simple.