It does indeed sound like Nan Huai Chin is speaking of the OOBE and immaterial domains, but there is also the implication of decent into hells after death, for those who cling, verses heavenly domains for those who do not cling.
On the breath. Most of those who meditate deeply do not have someone observing them closely, and historically there was no electronic monitoring equipment, so when one meditates to the depth of the 4th jhana one can no longer detect the breath; however, the breath will still be occurring, it will just be shallow, and slow.
Once I dated a woman who was a health professional. She awoke me several time in the year that we dated giving me CPR, because she thought that I had died, because she could not detect my breath, and I slept so deeply, when I was in OOBE.
Your oxygen requirement must have really plunged, I can't imagine waking up with someone pumping my ribcage lol! I guess that says that at least in fourth or beyond, external respiration stops or becomes shallow enough.
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A new thing I realized...
When meditating yesterday, I realized that if I am already experiencing the auditory charism, it takes effort to go back into the tingling bliss of the first and second jhana (was wondering if going from first to second then to third could help me go into deeper states). But it seemed as if I could experience full body tingling this time, not just the ear.
This time I took some time to explore the visual charism and under my eyelids there were lights flashing green, purple, orange, white, as if it were some disco ball lol. I've never really realized it because I always kept my eyes closed and turned my awareness inwards into my mind.
A few memories came into my mind yesterday after the session.
I realized that when I was younger, I would unknowingly go into concentration practice. I remember when I was in a German class, when I finished my exam, I stared at this pin in a noticeboard, and then I realized I could go into an extremely hyper-focused mode, where everything around started to become luminous, almost to the point of obscuring my vision, leaving just the pin there. At that point of time, I was a quite rigorously scientific person, so I dismissed it as excessive activation of the photoreceptors in the eyeballs. The pin that I was focusing on disappeared, that was why I thought of it that way. But the point was, this wasn't the only time. I kept doing it again and again, focusing on random things in the car, in the park, in school, etc.
I also wondered why I haven't experienced a really drastic "dark night of the soul", then I realized that when I was young, I DID have a period of such depression. I believe I was about five years old, and I fell into a huge depression, saying that everything in the world was just redundant and people playing in their own sandboxes. Economies, mathematics and even the concept of money were just stories they've created to entertain themselves and distract themselves from who they are.
Being a kid, I was supposed to be addicted to television, but then after that period I didn't want to watch anything to do with television. I sort of realized, as if I was clinging on to lights appearing in an orderly fashion from a digital box and found it so redundant. All I wanted was to "space out", but in a way where I could look inwards. This was when I started seeing visions of this extremely bright point of light. To this date, I still can't figure out what it is.
Then I remember recently when I had a really bad sleep, I woke up to this vision under my eyelids. It was similar to this...

Except it was almost like it was a kaleidoscope. The words kept radiating out from the center. I tried to read the words and it seemed like they were ... Sanskrit maybe? Perhaps I should take up the language of Sanskrit? I've NEVER seen this language in my life before, so it can't be memory from this lifetime at least. My inner guess was that it was Sanskrit, since it looked a little squiggly, but I may be wrong.
PS: I was trying to find the name of this thing so I could find a picture of it, and it was only yesterday when I went to another cousin's house that I saw a picture of this "mantra" arranged in this manner. Kind of coincidental. So I saw the word "mantra" below it and then managed to google an example of it.