Hopefully, you've gotten hold of the Vet by now. I certainly wouldn't wait until his appointment later in the week if he's getting so much worse!
Lyme disease is just awful around here. 25% of our dogs have had it...we know it when we see it now. Probably 25% of people here have had it too.
Have the Vet test for LYME and ERLICHIOSIS. They'll sometimes get both at the same time...
If you catch it soon enough, antibiotics and anti-anflammatories will make him feel better in no time...however, he'll need to be on the drugs for about a month to make sure it's gone.
Hopefully, you've got some better insight about what's going on today...please keep us informed!