I had a cavalier king charles spaniel puppy just die recently. He was properly vaccinated, parents had all of the correct health requirements, and he had a vet check just a few days before with my vet and was perfectly fine. On Thursday morning, I let him out to go potty and he was energetic. Woke up a few hours later to let him out again and feed him, he was very lethargic and not eating. He was drinking normally and his stool was solid No fever but his gums were pale, so I took him to the vet. Blood work came back with him having almost no glucose, no protein, and a high white blood cell count. It almost seemed like his liver and kidneys just weren't wanting to function. He was also anemic, keep in mind, 4 days prior, everything was great with the blood work on that vet visit... They kept him over night, ran fecals, more blood work, ran urine, and did an x-ray. Nothing was out of the ordinary. They did many tests but nothing was coming up. I told them to run everything they could think of and he came back negative on everything. After a while at the vet, they told me to take him home and they would run some more stuff Monday. He had one more check up on Saturday, they said he was fine. Saturday night, he was started to not show so much interest in eat but all of his other vitals were fine, stool was solid (like normal) and he was playful and energetic. Vet told me to just force feed him since he was still energetic and drinking water and I shouldn't worry.
I was awoken by him whining and then he started to have a seizure in his crate. When he was done, he had his head bent back and it wasn't much later before he was gone. They got the results back from the necropsy and the vet just told me it was fading puppy syndrome.
Keep in mind, the breeder has been very forthright and courteous through all of this. I'm just very confused by just saying it was fading puppy syndrome and leaving it like that. Have any of you had similar experiences? He really was such a great little puppy even though we only had a few days together.