I'd ask them what "hydro" meant. And perhaps if you took him in to get some sub-q fluids it would help dilute whatever is making him this way. It would probably be too hard to get an IV catheter in him, the way he's feeling. (It could be done, but not worth the wear and tear on everyone, especially him!) But having a couple techs to assist, a quick 250 mg. of fluid sub-q could be achieved in 10 minutes. Of course, this would require getting him into the car, so maybe it's not feasible.
If this is so "normal," then it's predictable, and they should have told you to expect it!
ETA: I know how awfully distressing this is for you, not to mention your pup. I'm so sorry. Prayers that it stops very soon!