PhatoseAlpha,
the "hallucinations of the brain" due to oxygen deprivation are the silliest, most un-scientific explanation. I take it you have never pursued this interesting subject yourself.
I recommend you read books by Pim van Lommel "Consciousness Beyond Life", the very good "Dying to be Me" by Anita Morjani and especially the "Journey of Souls" series by Michael Newton and the books by Chris Carter.
Warning, YES there are is a lot of crap in this niche and a lot of "religious" books, let me assure you those are not.
**
To come back to your argument that it's hallucinations, explain to me why people who have NDEs report pretty much the same experiences (with some distinctions, depending on their beliefs)..not some chaotic "hallucinations"?
Explain to me why people who have NDEs report ONLY, and ONLY to meet actual deceased people and why there is not one single NDE report I am aware of where a person "meets" living people or "fantasy people".
Explain to me how it comes that afterlife experiences are consistent and the same, for hundreds of years, across cultures actually.
*
By the way there are people who "scientifically" had been "dead", aka brain activity ceased entirely. There is a "famous" case where a woman had brain surgery, where they needed to "freeze" her brain, no brain activity whatsoever. (I am sure there are more such cases)
I am sorry, the "explanation" that NDEs are "hallucinations" is waaaayyy too simple to me, in fact entirely ridiculous. I urge you to read those books too.