I found a good response to these skeptic's "explanations" of NDE's in Dr. Ron Morse's book "Searching for Eternity".
He responds to several different "explanations", but I'll share the one having to do with what you're describing (lack of O2).
From his book:
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5. The Lack of Oxygen Or Excessive Carbon Dioxide Theory
The Concept
Brains lacking oxygen or with excessive carbon dioxide produce hallucinations.
The Rebuttal
Various studies have actually found that the brain lacking oxygen or with excess carbon dioxide produces chaotic hallucinations that abound with disorientation, confusion, and fear (as with mountain climbers or fighter pilots). This contrasts with the NDEs in which calmness, tranquillity and a sense of order predominate. In addition, cardiologist Michael Sabom has reported on a patient who had a NDE and had his blood evaluated during the experience. It revealed high oxygen and low carbon dioxide. This is probably why most people who come out of their NDE are able to give complete and cogent reports of their findings. With many accident victims, there is no oxygen-depletion and yet they have had NDEs.
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Morse, Ron. Eagle Wing Books, Inc. Memphis, TN. 2000.This is the 5th of a total of 12 different skeptical claims he has a response to. I recommend the book.
Actually, seeking_answers, I highly recommend it to you. Dr. Morse was someone suffering from death anxiety and went on a "quest" to see if there was any truth to the claims of an afterlife. His conclusion was that in some way, shape, or form, there IS.
Realize that there will always be doubters, skeptics, non-believers saying they know or can prove that there's nothing after death, so if you're goal is to convince all skeptics in order to convince yourself, or you want to find a way to knock every claim out there, you will never stop looking. They will always cook up a new one if their current ones are shown to be false. Ironically, they're quite similar in behavior to the believers they seem to dislike and disagree with so much.
Just try to reach a conclusion for yourself (or, if you're like me, your best guess) and try to find peace with it.
It's the human race. When have we/they EVER all agreed on something 100%? It just doesn't happen.
I was an athiest with death anxiety and started a similar "quest" to Dr. Morse. It started almost 3 months ago. I'm far from finished. FAR from it.
But honestly? While I don't KNOW if there's life after death, I SUSPECT there is and I think it's more likely than not.
That's part of the reason why I came to this website and decided to join this community: To learn more to refine my suspicions. I'm still far from finished in my "quest", but right now I feel reasonably comfortable in my suspicions. I'd like to feel better than I currently do, but it's not bad where I'm at so far. I feel okay about things. But there's still much to explore.
Definitely check out this book. You may not agree, but you may find some things to chew on.