If his blood work and medical tests came back normal can they rule out a spider bite or bee sting, or something that may be causing a localized allergic reaction. I don't know a lot about this stuff but my last pup came down with significant lethargy and it took some time to figure out he had been bitten by a spider. Just a thought. Good luck figuring it out.
Dante (GSD) Feb. '05 - Apr. '13
Ruger (GSD) Dec. '13 -