my cat has been having similar issues, I went away and when I was back she'd lost abit of weight, since then shes not been able to keep food down of any kind and developed deeper breathing, my thought was because of being so tiny in the first place and now so thin shes since been to the vets and discovered shes got fluid round her lungs, hes taken a lot away, and without proceding with any further tests, which will be more invasive right now plus cost me ALOT, we don't know the specific cause , shes had a dose of antibiotics and got some diurectics to be going on with for a few days to see if theres any improvement............. I just don't really no what to do at this point, any advice will be really helpful the vet said I could be a tumour or a cat disease (forget the name!) but shes an indoor cat so cant see the latter being it! he says he doesn't think its her heart, shes very sleepy now, and has been able to keep down the vet food sent with her home nothing else! any advice? I really want to know why, but the vet said its basically if she reponds to this then it would be something they could treat if not........... so idk