Thank you Daniel, SO helpful!
I add something from my post in the Kenneth Dharma site, which seems more meaningful after your reply:
"After deep meditation session there is always something going on, this time I was in a A&P (easy noticing, bliss, the good stuff) but after a while the sense of an happy Watcher faded and I was no more than a process going on with no self. I had only the time to notice that I was observing anatta in real-time (which I believed develops only after fruition) that a real fear of losing myself arose, I tried to recollect a strong sense of a Watcher at all costs. The good thing was that this fear too arose and passed away. This was the first psychological side effect in my meditation (other than piti&sukha ), I believed I was exempted and could experience the dark night as only an energetic process..."
I dont'know if it really was the fear stage, but now I'm pretty sure I'm always dealing with the A&P territory and boundaries since this march.
The reason why I was thinking of being in equanimity is that sometimes I end in a jhanaic state which is more spacious, quiet and delightful than the A&P/2nd jhana. So I started to believe it was a soft fourth jhana.
I was able to distinguish four different restful state, but maybe I'm only bouncing between 1st and 2nd.
In fact, trying to travel up and down the jhanaic arc, I noticed that this soft 4th jhana could be the second as well...

About the jhana thing, 6 months ago I had the weirdest jhanaic experience, a very one-pointed concentration (different from the lazy one that is my usual habit), a sense of space and the head becoming bigger and bigger, like a balloon, and a more 'mental' component (promptly, my indulgent self-assessment sorted it out as a formless one that I could label as INFINITE HEAD...).
This stuff returned only once 2-3 weeks ago, and during my last two meditation sessions. Now it builds up out of nowhere, at the beginning of the meditation, and I'm just locked in (but there's no more fun), even with lazy concentration. When it fades gradually the head deflates... and I'm out of meditation.
About the practice: last year I went to a 10-days Goenka retreat, but after a while I abandoned the sitting posture and developed my own lying-down meditation, which is choiceless awareness-like, with a natural focus on physical sensations (Goenka legacy) and sounds (it is very easy and fun for me).
When I discovered Shinzen Young teachings (thanks DhO) I just tried to add this flow/gone alertness.
I don't use noting ala Sayadaw because I feel unconfortable with 'procedures' (like Goenka's body scanning).
So my practice is kind of home-made, I don't know if it is consistent enough to progress.
My aim is to practice only Theravadan shamatha/vipassana. This lucid-dream-like-state during meditation came on his own, I'm not trying to provoke it.
I wasn't sure how to interpret the melting of wandering mind&lucid dreaming and the images arising after sensations, which are new stuff. Is it a sign of progress of just 'stuff'?
There is also this 'muddy' state, a wave/stream made of dissolving thoughts, physical sensations, images arising, confusing but somehow 'deeper' than A&P.
Any suggestions welcomed.
Umberto [Edited for further details]