Hello everybody, that's what I experience:
(resembles a little the description of the impermanence & no-self door in MCTB, but I don't know what the unknowing moments of the A&P look like - but as far as I can say, it's only one moment that resists cognition)

Somewhere (usually to the top right) something starts strongly shaking everything I see like an earthquake, ~4 Hz. Within 2 seconds I turn towards the center of these shockwaves and await it, ready for anything, it comes (smiling) towards me and shakes me. I bounce towards it and away from it with very strong sense of acceleration (feels like 4g), but what is moving is not my body, but the whole space I am sitting in. This happens 2-4 times, then my center hits the epicenter of the spacequake. I loose sense of direction & space and find myself in a very very peaceful and clear state where all limbs feel very slim, out of proportion, but beatiful. My body tastes blue.

If you like this image, I am a ship on the ocean, I feel a big wave come, turn towards it. The wave is several times bigger than my ship and makes it overturn, I don't know what happens, and then I am underwater, it's nice and silent and I am sinking to the ground.


Now where and how does it occur?

Most times it happens when I am lying on my back and relaxing. In 2008 it happened first, and repeated every 3-10 weeks, though I did relaxation daily (and still do). I associated it with access concentration then and didn't percieve the shaking. I never knew what hit me. Or from where it hit me. Or how to get into the silent state at will.
In july 2009 I had an extraordinary joyful time (A&P maybe), and this phenomenon occured almost every night before falling asleep for 2-3 weeks, and every few days when relaxing during the day. Don't know if the joy came from jhana, or the jhanas and joy from a part of the cycle. After these weeks, these experiences started getting rare. Along with the good time in july I had first results with kasinas in entering jhana, and at least these are still available.
I really liked the tranquil state before falling asleep, thought that I had learned it more or less now, and labeled the state 1st jhana. The clearer perception of the entrance came with the repetition. A good way (the only one I found out) to trigger the spacequakes was focusing on the vibrating back of my eyelids, then on the space in between me and the eyes or beyond them until the shaking started. The shaking seemed to be a necessary part the state shift.

Now I could not reproduce it for weeks, and the few times something started shaking, I would turn towards it, but dodge it in the last moment. Out of fear. I couldn't throw myself into the epicentre, and so it would fade without myself enjoying the blissful state afterwards. I do not know what has changed since july, the fantastic days I had then are past. Not that the world is not beautiful now, I but I wouldn't mind being overturned every night again. I don't know why I started holding back lately and what I am afraid from. Ok, it's a little creepy, but I miss the experience a (amongst the strangest things that have happened to me) and would like to understand its significance.