I think I've accessed what Thanissaro Bhikkhu describes here, in fact I'm pretty certain that this is the case, and it was done through working with yoga nidra.
there is an common set of distinctions drawn in vedic- and brahminically-sourced traditions between the (ordinary) waking state, the dreaming state, the undreaming sleeping state, and a fourth state standing in ambiguous relationship to these others, and some context these distinctions are presented in may, i speculate, be relevant to your inquiry.
The fourth state Tarin is talking about is called turiya (depending on which tradition you're talking about), which is something like a conscious but dreamless sleep. I've definitely experienced this on several occasions and always through one-pointed concentration (which may be why this is not right concentration?), you remain completely aware but there is absolutely no perception occurring. It doesn't seem to be the same as 8th jhana, although I couldn't say with any certainty. I was accessing this long before what I believed was stream entry so I could be miles away but the descriptions given seem very, very similar. I can't describe what happens
during this but I'll have a play around and see if I can get there again to investigate it properly.
One big thing I've found, through being shoved, poked and prodded by my partner when I've gone into this 'state', for lack of a better word, is that the body appears as if in a deep sleep and can even begin to snore. Afterwards, I have absolutely no recollection of making any sound, or being touched and long periods of time could have elapsed which, subjectively, feel like minutes.
I could be very wrong but I thought it was worth mentioning.
Edit: I've been looking at some material on turiya and my understanding may be incorrect, it's possible that what I'm talking about is the stage before turiya. On the other hand, when I experienced this before I had no knowledge whatsoever of insight and had been doing intense concentration practice so it may be that I just didn't see it correctly. No idea.