In-between the seventh and the eight sit, on the day of the eight, there was some very fascinating stuff happening with the body.
If you haven't read the thread on KFD on
Tummo, I suggest you do. It is very interesting!
Anyway, how does that relate to what happened with the body? I don't remember all the specifics, but here goes:
I was compelled to lie down on the floor to relax a little. Lying there with my arms stretched wide open, embracing the universe, I noticed that if I stretched a certain muscle running down the side of the body by the abdomen, and I stretched it in a very peculiar way, involving retaining the breath in some way, I got a really good feeling in the solar plexus area. I proceeded to do this on the other side, really getting into it hardcore yoga style.
What this lead to was some progressively more unusual breath retention and muscle stretching exercises that I've never ever before seen demonstrated (and I can't say that I remember any of the instructions in the Tummo thread) by anyone. It just all came to me, ancient knowledge of the sages I guess

As I stretched those side muscles there began a contraction of the spine, somehow connected to a breathing pattern, that sent the body into very intense/violent and rapid shaking (as described in the Tummo thread, if I remember correctly). It actually felt really good.
Things got "curiouser and curiouser", and focus moved downwards towards the pelvis area and energy/breath in an empty space under the belly. Really cool stuff happened. There was a point where it felt like I was breathing bliss with the penis. Yes, this sounds very strange, but I can't tell you how awesome it was. If I were to take a stab at guessing what this was then I'd say that I was seriously messing with sexual energy in the body. There were many other aspects to this, penis-breathing being only one small aspect. I don't think I've ever held my breath as long as I did today or stretched those muscles (many more than the two on the sides that I mentioned), and the craziest thing is that I didn't even feel like I was doing anything - the body just kept doing more and more interesting stuff.
I reached one point that seems to line up with what I remember from the Tummo thread: there was a time where everything was very quiet. It was after a long exhale, (which was preceded by some seriously deep breaths) and I wasn't breathing. This thing is supposed to be an awake version of Cessation, if done correctly and my memory isn't failing me.
There's much more to this than what I have written here. I might have been doing this (without actually feeling like I was doing anything) for about 45 minutes. I get a nice feeling just thinking about it.
If any of this sounds interesting to you, then I would recommend reading that Tummo thread. Not because I followed any instructions from there, but it seems that the instructions in that thread is at least aimed at the same things, and those things were awesome. Actually, I think I might go do some more right now

EDIT:
And I should add that I was never into sexual energy, prana or any of those hocus-pocus-things. But damn, it works!