A few months ago, my 16 year old neutered male cat spent a weekend acting sick, vomiting, not eating as much as usual. We were going to call the vet that Monday, but he started acting completely normal Monday morning and we chalked it up to a stomach bug.   
  
He's also been eating less overall over the last six months, and has lost weight,  but we thought it was related to a tooth extraction he had around that time and some subsequent skittishness around his food, and we were trying to remedy it. We got him onto a brand of wet food he would eat more reliably and started buying smaller bags of dry food so that it would be 'fresher'.   


Starting last week, the vomiting and lethargy symptoms came back. We took him to the vet and got bloodwork done. The vet suspected kidney failure, but the test wound up showing indicators for failing bone marrow (low cell counts, etc).   
  
The vet said that short of carting him to a specialist two hours away for a bone marrow biopsy (which we are not going to subject him to), it's impossible to know for sure what is going on, but his theory, based on what he's seen in other FIV+ cats, is that the virus is entering a progressive phase where it is more aggressively attacking his white blood cells and affecting his bone marrow, and given his age and some other medical issues he has, it is unlikely that his body will be able to rally from it long-term. 

He has perked up since the vet visit, but we know it is likely only a matter of time till he declines again, and we want to be proactive about preventing suffering for him. Has anyone else had a similar issue with their cat?