I totally know that feeling. I think it is the feeling you get when someone who truly cares about you touches you. The feeling of being on the receiving end of the purest kindness. That's why you feel it from certain doctors (and maybe not from others). One of the times I felt it the strongest was on a kind of meditation retreat, and my teacher was telling me something and he touched my third eye point, and I felt a warmth go into my head, and then it kind of sank down and turned into that feeling, a sort of lightness and warmth in my solar plexus and chest, moving up my spine... That particular time the feeling lasted a long time, too, and I think that was because I was so open from the meditating.