OK, it's not necessarily thiaminase deficiency. Whatever the cause, the symptoms described are far from encouraging.

The trouble is that so few snakes get a proper necropsy that cause of death is rarely determined with any certainty, so the prevalence isn't clear. . The symptoms and history could fit thiaminase deficiency, it's something I've not experienced first hand and hope I never do so I can only go with descriptions I've read. Maybe other causes fit the symptoms as well. Richard threw out a few ideas for possible causes, but mainly put the symptoms down to a snake in extreme pain (I fail to see how the symptoms didn't sound like a neurological problem), that is a cause that can be proved as easily as thiaminase deficiency.
In the circumstances described by the OP there really are two options - get it to a good vet, or watch for the progression of symptoms and be prepared to euthanase or watch it die.