I don't understand how you can say it can be briefed and not trained for and would be interested in further discussion. In my experience, no amount of briefing would prepare you for the sensation
I think Dan is trying to say that you can't generate the leans or SI in a training environment but have to rely on been briefed that such things exist. Like you Akro, my first experience of the leans occurred with an instructor (the same one as you I assume) and I was able to tell him that all wasn't well in my mind and he talked me through it. Since then I've had the leans a few more times but once experienced, straightforwards relatively to deal with.