I like that term being "in flow". I used to hear the term being "in the zone" when I played tennis as a kid. One coach told me I needed to "be the ball" (I'm guessing this is variation on some Buddhist all is one motif). Though I never achieved that state as I never really liked tennis. I wonder if one type of happiness is finding that activity you enjoy enough so be able- eventually- to be "in flow" or "in the zone".