Autonomous Sensory Meridian Response (ASMR) is described as a pleasurable, tingly sensation in the (back of the) head.
The sensation can be triggered by a vast variety of stimuli (auditory, visual, olfactory etc) but seems dependent on attention. It seems not everyone can get this sensation and among those people that do, stimuli that trigger the sensation vary considerably. See also:
But what could be the physical origin of this sensation? And how come only a select group of people seem able to experience it? In http://theness.com/neurologicablog/index.php/asmr/ the ASMR sensation is proposed to be caused by either  small seizures or  extra sensitivity or extra 'pleasure-shots' to stimuli that for other people are just moderately satisfying. Other sources compare ASMR to meditation.
Does anyone know more about this phenomenon, or have another theory about the mechanism behind it?