I've been playing with 5th-8th jhanas, and my preliminary experiences seem a bit different... maybe they are just incredibly soft at the moment? I say the term 7th and 8th jhana here without qualifiers, but I am not sure that I am labeling them correctly. however, since they are different than the previous ones in a noticeable way, and they follow 5th and 6th ones, it seems about right. I'm curious if others' experiences correspond more with my descriptions, or MCTB ones, or more classical sutra ones. In any case, let me know about 7th and 8th jhana especially, as that really differs, and let me know what it is if you know.
5th Jhana pretty much corresponds, with space seeming to expand. I focused on this last night and managed to get it to expand more than it has before. My sense of body is still quite present, though. Also I tried expanding the space around my body and felt a coolness around the areas I was focusing on. Also I was seeing color swirls and stuff that I've come to associate with insight practices.
6th jhana I haven't gotten down too well, but mostly I feel like I go into the space, or that I'm kind of holding the entire space in the palm of my hand. It's more present all-at-once. I might also project a tingling onto it that I guess I can call "consciousness" that seems to expand into it.
7th jhana takes 6th jhana and kind of "flattens" it out. so while the level of space expansion and consciousness expansion is where it was at when I left 5th and 6th jhanas, it just feels very flat and dull. There's also a kind of background light to it. I still see color swirls, though faint ones, and my sense of body is still present, though a bit diminished. But after sitting for 15-20 mins or so on my shins and feet, I started feeling it hurt a little, though nothing too distracting. My sense of self is not "extremely subtle", though, as I still feel very much there. My overarching description of this would not be "nothingness", but more like "flatness" and "lack of perception of what's in the space so clearly as before".
8th jhana takes the flatness of 7th and makes it "murky". That's the best way to describe it. Instead of flat and clean nothingness, the whole area is just like a black fog or sludge shifting about slightly. The claim of "There is no reasonable way to attempt to describe this state, save for that it is a mind state, and thus is not emptiness, as emptiness is not a mind state or anything else for that matter" is not accurate here, though, as I think this description is pretty reasonable =P. There is still a sense of me, and a sense of my body, and still feeling some sensations on my feet which must be hurting by now. Instead of feeling "pain" it was more of a "hmm I should get up shortly, as something is probably not right there." Again I disagree with this paragraph as well:
It is not possible to investigate this state, as it is too incomprehensible. Thus, as this state ends, the meditator may return to lower states or turn to insight practice in the afterglow of this state. It should also be noted that, in contrast to the previous seven jhanas, the issue of “hard” or “soft” jhana that relates to how solidly one is in a state does not apply to the eighth jhana. You are either in it or you are not.
Also in all these states I still had thoughts popping in and out. I actually feel like my concentration has not gotten that much better since SE, just that I can access these states now for no particular reason. As a random aside, I think it would have taken me a really long time to cultivate these without SE, so if you want to get these states fast, get SE first, as others have also recommended to me.
I then decided to exit in an orderly fashion, going down the jhanas in order. I thought my sense of body was still pretty much intact, but as I got lower and lower, the sensations in my body grew in intensity. On hitting 4th I felt my legs more clearly. On hitting 3rd, with the cool joy-bliss instead of coarse body-bliss, my feet started hurting. On 2nd and 1st it intensified and I realized I shouldn't sit like this too long in general.
Also fun was that I could focus on "access concentration", and just notice the breath with no jhana, and even after that I thought "no concentration", and my breath was not clearly visible as separate anymore, and felt just as another part of my body. Focusing on not focusing?