I'm the most un-still person on the bike. I see my support videos I'm wriggling like a snake to keep moving . Head shoulders a slight bob. May as well finish destroyed than " I could have gone harder". Not a racer of any kind , just 100% committed to myself & the bike when on it.
It can be a good thing. The best racers in TdF tend to move a lot while pedaling too. More than what I see in many recreational riders. Perhaps because pros spin bigger gears.
As long as you're not spending any effort to maintain posture and the extraneous motions are purely to exert more force on the pedals, you're good!