I've been reading these discussions and gotten some comfort. Our 7 yr old golden retriever just died suddenly, and it's driving us crazy, so I have to ask the same question.
Copper is a big (95lb) golden retriever, healthy except for a small tumor removed a year ago. He got his routine vets checkup June 15, and had a clean bill of health (including palpating the abdomen, where the tumor was).
4 days ago, we noticed in the morning he had not eaten his dinner. He showed no other signs of discomfort, no vomiting etc., so we watched, but thought it might just be loss of appetite from the heat (It has been very hot here, and he seemed to be avoiding the outside). So we let him rest, gave him lots of cold water, which he drank well. I hosed him off that evening outside and noticed he did not shake the water off, something he usually does enthusiastically. That evening, he sort of declined to go on a walk with our son, so he tried again in the morning when it was cooler, but the dog did not want to go then either. I took him for a walk in the afternoon, hoping he was feeling better (this is the 2nd day since he didn't eat dinner), and he went very slowly around the block, but peed and had a bowel movement. That night he started labored breathing, we took him to the ER, and he died in our arms.
We are all devastated, and were so shocked we buried him the next day and did not think to bring him to the vet for a necropsy. So it's driving us crazy. Can anybody put 2 and 2 together on this? I thought it might be GDV (twisting of the gastric tract), but he was missing one symptom, bloated stomach. But in retrospect, the failure to shake his fur coat after getting wet might have been significant. Help us understand if you can.