The short of it is that Rocky stopped eating. He'd drink his water, but he would often throw it back up again. We gave him medication for nausea, so he didn't get dehydrated. He just wouldn't eat. On Friday Rocky had become too weak and disoriented to walk, so I had to carry him into the veterinarian's office.
I've written about Rachmaninoff in several places. You can read about how we found him here: Doggie in the Window. I miss him terribly.
The only downside to owning a dog is that you'll very likely outlive them.