If you can, get the vet to do a blood test and test blood pressure. Ask for the results and join the forum connected to the link I sent, a really excellent source of info and support. The cat could need fluids rightaway. Your cat sounds ill, but also as if it hasn't "crashed"? Keeping a sick cat fed and hydrated is really crucial. Most cats can't resist the water that comes with tuna in spring water and you can dilute it farther to get them to take in a bit of liquid. (no tuna in brine though.) Because cats evolved as desert animals, they don't easily drink enough, especially if they have CKD.