[cypher]

I'm really sorry to hear your ham is not well, it's hard to guess what may be wrong with the symptoms he's showing & the rapid change in weight.
Has the room where his cage is been kept warm at all times, day & night?
I don't think there is much you can do until you can get him to the vet other than keep him warm & comfortable, probably best left in his nest for now or in a carrier with plenty of substrate if you want to keep a closer eye on him.
You could try offering water with a syringe or spoon or just hold the bottle for him to see if he needs to drink, you could also try some cooled porridge/oatmeal on a spoon to see if he'll take that.
I hope the vet can help & he'll be ok.