What is the proper name for this phenomenon and how common is it. I fear this question will be meaningless to anyone who had not experienced the phenomenon firsthand.
I refer to the semi-trance state one can be precipitated into by (for instance) the slow repetitive actions of someone in very close proximity, someone who will be either oblivious to your presence or totally disregarding of it.
I guess the phenomenon shares common ground with hypnosis except in this state you remain in control, albeit in a very relaxed state. Other than that, the only physical accompaniment to the phenomenon is a characteristic tingling of the scalp.
The experience is altogether a pleasant one and whenever it occurs I will remain still and receptive, reluctant to do anything that may bring it to premature closure.
The other question would be, is this experience an incidental side effect of some useful physiological response, or what could be the evolutionary imperative that led to it and still preserves it in some people?