Two of my 7 cats died in the past two weeks. They had the same symptoms. One died in 2-3 days and the other overnight. I am concerned with for my remaining 5 cats. It starts with laying around very listless then vomiting what looks like a large hair ball with brown liquid around it and urinating on themselves. For a short while after this they acted like they felt better and then they died. What could it be?
Based on your description of the symptoms, I am most suspicious of an infectious cause or exposure to a toxin. I would recommend a thorough evaluation of your home and the cats' environment. Is there any possible access to medications in the home or chemicals outdoors? I would also recommend that your other 5 cats are evaluated by your veterinarian.
A thorough physical exam and consideration of screening lab work, such as complete blood count and superchem, would be ideal to investigate a possible infectious cause of these symptoms.
If another one of your cats becomes ill or begins to show similar symptoms, that cat should be evaluated by your veterinarian immediately. I would also consider pursuing a necropsy if another one of your cats should die with similar symptoms. These steps may identify the cause of these signs and help prevent additional illness in the future.