Sudden onset of this sort of symptom in two snakes at the same time strikes me as being too much of a coincidence.
Heavy metal poisoning takes time to build up, for both snakes to develop critical symptoms at the same time would be odd.
Vitamin / mineral deficiency would be similar, too big a coincidence for both to go critical at the same time.
Sudden critical neurological symptoms would be something I'd think off as being poisoning, that means something in the food or environment. Is there any chance someone has cleaned or polished the furniture near the viv and they've got a blast of some sort of aerosol?