Sounds a bit like a subjective experience. Do you maybe mean the 100% focus one sometimes (or most times) experiences in meditation? I guess its natural that we get out of this focus when we stop meditation, at least for non-enlightened.
I guess the breathing rythm you mean, is the natural rythm of your breath. By letting go of the need to control your breath, you probably get into this rythm.
Just my 5 cent,
Phil