I once had an old snake that was given to me (unwanted) that ate good but never moved around much (even to defecate)...she didn't present any neurological
symptoms (like spasms) but when my vet x-ray'd her, it showed she'd had a back injury. Still think an x-ray might be a good idea, pity your snake scared the vet.
Snakes that are put on the floor/ground frequently feel extremely defensive because suddenly we're looking so huge & menacing...it's typical for snakes.
I was thinking that something happened to this snake before he was given to you, maybe a fall, or a chemical exposure, but the way the symptoms are increasing
makes me wonder about other things that could be going on too. And remember that when animals are re-homed, previous owners frequently either don't tell the
whole story (if they know), minimize what issues they know about, or have no clue what's going on either.
Sounds to me like maybe a second vet opinion, someone more experienced with snakes? No way we can tell you what this is...only help you speculate here.
BTW, don't use Pine Sol around snakes (fyi & I'm not saying you did)...it's in the same category as cedar shavings, very irritating & likely toxic to snakes etc.