Autonomous sensory meridian response.
wiki
Ever experienced this? If so, what are your triggers?
I get it when I'm close to two people having a quiet conversation. Like when I'm at my desk and I can hear people in the next office speaking in hushed tones. Also, randomly, when I hear a recording of Jeff Buckley singing Hallelujah. I have some others but I think you get the idea. If you're not sure pull up a couple YouTube videos by searching ASMR. There's this chick Athena Jezik (sp?) who makes these massage instruction videos (which I came across when I was legitimately interested in some techniques).
Anyway. It's awesome.