My name is***** and I would like to help answer your question. First, let me say how very sorry I am for the loss of your beloved companion. I know first hand just how difficult losing a dog, and family member, can be. Golden retrievers are sadly very susceptible to neoplasia (cancer), and the risk increases with age. Based on the clinical signs, one consideration would be a systemic cancer such as lymphoma. Lymphoma can affect the stomach and intestines, leading to gastro-intestinal signs (soft stools, etc). It can also potentially spread to the spinal cord leading to instability and eventual paralysis. Certainly in later stages, patients can also stop eating and become lethargic. Symptoms of lymphoma can occur slowly or rapidly, depending on how advanced it is on diagnosis and also the grade of disease.
Of course it is impossible to say what exactly Sam was suffering from at this point and certainly other types of cancers are possible as are systemic infections (bacterial, viral, or protozoan). Typically with signs that are affecting multiple organ systems, however, lymphoma has to be high on the list.
I hope this helps, and please let me know if you need anything else at all.
Thank you for your prompt reply. We are happy with your comments. We were never told by our vet that he could have cancer but he was very poorly during this last week and was taken to the vet only last Thursday, By Monday afternoon it was very clear that he was seriously ill so was taken to the vet who put him to sleep. Because we were so upset to lose Sam we never asked any questions and only now are left saddened and wondering what was the cause of him having to be put to sleep. He was a beautiful dog and was a huge part of our lives. He will be missed,
Thank you again