He refused food and was straining and producing a couple of drops of urine each time. I know urinary tract blockage is a serious condition for male cats so I took him to the emergency vet. But they couldn't find a blockage, so they took an X-ray. It turned out the problem was with the other sort of elimination - he was chronically constipated.
They gave him an enema. Then they had to wash him. Then when I got him home, I had to wash him some more. Poor guy. I also have to switch him to high fiber food now, or add pumpkin or metamucil to his food.
I had no idea how lucky I was with my cat Selkie, who never had a single health problem until the last couple years of her 12 years with me. Both of my cats have chronic problems now. At least Biscuit's vomiting episodes seem to be staying under control with application of allergy pills.