Your experience is that which is starting to sound "typical" with all the options. It does appear that "novel" soft stimuli are the key and that might be a clue given that novelty seeking behavior crops up around discussions of dopamine.

Not to stretch things too far, but thee is a possibility that two different things have been discovered here. The one described so well in Zflwr's post and another that I experienced when standing with bands on my thighs. I reported it earlier but, briefly, I found that the time that I could stand up while fishing went from a half-hour to four. The sensation was such that I believe that my muscles tensed slightly in response to the bands and my muscle tone was protected. The latter was protective and the former was corrective.
-Rick