Aha, thanks everyone.

I believe I was about to experience something similar last night as well, I remember telling myself in some trance-like state that "now, let's re-enter that last dream..." and then I got a feeling I was watching some dark rectangular object or whatever, almost like a blank dark canvas, and tried to "dive into" it.
I don't remember anything after that, but in any case it was apparently an enough unusual experience to leave an impression on me.