Yeah Mo, we use to call it 'in the pocket', but that term has become so overused (and abused) that it no longer captures the feeling you've described. As I've gotten older, those nights of being in the 'groove' (usually only happens on ONE tune during a set) seem to happen less frequently. This could be partly due to the booze/weed-free sets we now play

. But when it's cookin', baby, it's cookin'. BTW, I've often wondered if that 'feeling' we're talking about, ever happens in anything other than jazz and R@B. Not a put-down, but I just can't picture it happening playing polka's all night. But I could be wrong.
chas