DISCLAIMER: I'm not a vet and I have no veterinary or medical background whatsoever. This information on liver disease in dogs is not meant as a substitute or replacement for veterinary advice. It's meant for educational and informational purposes only, as a starting point for discussing the diagnosis and treatment of canine liver disease with a qualified vet.
My dog, diagnosed at 15 with significant liver damage, primarily suffered from inappetence (lack of appetite). His energy level was great and although he did suffer from bouts of nausea, once he was outside he was his usual happy self. Unfortunately, due to his liver disease, he also suffered from hepatic encephalopathy.
With him, the first subtle signs started showing up about a week after his diagnosis. At first it was small - just a tiny stumble when he was running. Then I would notice little things, like a touch of unsteadiness, especially as he was coming down the stairs. Less than 2 weeks after I first noticed these subtle signs, they became more pronounced: he seemed a little "drunk" - a happy drunk, but drunk nonetheless. And yet sometimes he was perfectly okay. It was confusing. I called the vet.
He was prescribed lactulose, which acts as a laxative. Why is this important? As it was explained to us, a damaged liver can't properly process the ammonia in foods. A healthy liver processes the ammonia and renders it harmless. A damaged liver is unable to do this, and so ammonia levels build up in the bloodstream and circulate throughout the body. This affects the brain as well which can in turn cause these neurologic symptoms.
Anyhow, the lactulose appeared to work. We were told to give our dog enough so that he would defecate 2 or 3 times a day, and his stool was to be soft but not diarrhea. Frankly, it took a bit of experimentation and juggling to get it right (I'm still traumatized by the sight that greeted me on the day I gave him too much!). Once we got it right, my dog's symptoms completely disappeared.
I should also note that he was also prescribed an antibiotic (again, I won't name it as it's better left to your vet) that was supposed to reduce the bacteria count in his intestine. Perhaps that helped too.
Hepatic encelphalopathy in dogs with liver disease apparently isn't an uncommon problem. If you notice your dog showing symptoms, tell your vet right away - perhaps the symptoms can be alleviated and his quality of life improved.