You might want to take in a urine specimen. Skye never presented like most dogs with UTIs, but would start acting strange. Her vet learned to just run the test and would sometimes be surprised how bad it was. Seniors in nursing homes react strangely to UTIs as well,and their doctors more routinely check them.
And, of course I'll mention Cholidin. The description of Zisso trying to get under your desk concerns me. For Skye, the smaller the space the better and she would even try to squeeze under chairs. Cholidin was a life saver for her the last couple years of her life.
I hope things get better quickly.
With approval of my friends:
Seiko, Solo, Sophie, Skye and Buddy - bridge dogs who taught me so much