OH, is that what you call it? I've been aware of this feeling since I was little, but I never really thought about what a scientist might call it. I didn't even know it was such a weird thing, I thought everybody got that sensation sometimes, no different than the feeling of being grossed out, or tickled, or whatever.
Interesting, I'll have to bring this up to my friends and see if they know it too.
For me, ASMR is usually auditory. When I was a kid I used to listen to cassette tapes of this guy named Jim Weiss tell children's stories in his very soft, slow voice, and it gave me that sensation a lot. They were great for putting me to sleep, now I know why. It doesn't happen as often as it used to anymore, and sometimes I like chasing that feeling, trying to will myself into getting a tingling chill down my back. It even makes me shiver involuntarily sometimes.
Weird stuff, now that I think about it.