Sounds like your dog was suffering from an exposure to organophosphates. That is a chemical found in numerous gardening insecticides. Was any neighbor or even you treating your yard or garden recently? One of the dead giveaways for organophosphate exposure is what we call SLUDGE in the EMS world. It means Salivation, Lacrimation, Urination, Defecation, Gastric Upset, Emisis. I’m so sorry this happened to you and your fur baby.
I would never need a vet cos I cant imagine replacing my family member with a DOG...I wanted to know what caused the death because if it was an illnes I couldnt do anything about it, but if she was poisoned I could have helped her somehow, I wanted to call another vet but we were ashured that it was only a feaver and i was thinking it will all be better soon but....she kept looking at me and she was asking for help and I was simply helpless, thats what hurts me the most...she expected help and I let her down!
A house call from a Vet? That is unheard of in my limited experience. Fortunately we have a Vet about 2 miles from the house, still even in an emergency I am sure we'd have to bring out dog in... much easier with a 20 pound Westie such as we have.
My first though was poison, but I have no direct experience, I am happy to say. Still I could relate to your pain as we had a 90 pound Golden Retriever that went "down" before my eyes. He didn't die at that time but was initially paralyzed in the rear legs and it too several months of water swimming (done DIY) to regain enough strength in the rear to take care of toilet needs and move around, even up a couple of stairs on which I put non-slip treads.
In this case it was diagnosed as a stroke, not brain, spinal I guess affecting just the rear muscles. But, he went down and I saw and was too his side in a minute and noticed he was discharging some fluids from his mouth, too long ago to remember or even want to remember. I got a neighbor and we picked the Golden up and put him in my lawn/garden wagon that has drop sides, making it possible for us to move the big fellow around. We loaded him into the back of an SUV (it too two of us, both older males) and took him to the Vet. In this case the dog did have a partial recovery, but that was about 5 years ago and we had to put him down about 2 years later because of cancer. He was 12, which is old for a Golden. Remember, large dogs in general have shorter lives. I share this in an attempt ot give a possible line of research, a stroke.
I believe a German Shepard has a similar life expectancy to the Golden, but 7 is getting old I think.
I'm so sorry for your loss. I don't have any experience with an illness like that but I would definitely NOT go back to that vet. He obviously either doesn't care or doesn't know enough to help you when you need him.