I suggest you read this,
Amazon.com: The Demon-Haunted World: Science as a Candle in the Dark (9780345409461): Carl Sagan, Ann Druyan: Books
It's very important to be skeptical about 'unique' accounts. Just look at all the people the church made Saints for because of 'miracles'. People just tell what other people want to hear sometimes.
Line me up 100 hardcore atheists who all report the same experience and have very dissimilar lifestyles from around the globe, then you might be on to something. Even then, what we're on the trail about is probably just how the brain works and has no supernatural bearing what so ever.
I will say this. When a person dies, the pineal gland releases DMT. The same process that happens when you sleep, not the same amount obviously. Even then, the fact that most of the accounts of near-death experiences are similar is something that makes me wonder.