I don't know if moving him back will help. I just moved my girl up to a 28 qt tub and she went from mild head bobbing when cruising the tub to full on corkscrewing/ spinning etc. It freaked me out a little >_<

YouTube - Spider ball python- stress related corkscrewing / wobbling / spinning

I found that putting crumpled newspaper helps a lot. I would just try to make him feel secure- give him a hide if you typically don't give hides, crumple news paper, etc. He may or may not go back to how he used to be.