Cats often don't give us many clues that they are ill. Perhaps they miss a meal or hide in the cupboard. Perhaps they look for a cuddle; or perhaps they want nothing to do with you. Some will vomit or have diarrhoea. The occasional one will show pain by hunching over or curling up and wanting to be left alone.
Many of these vaguely ill cats have pancreatitis, a painful inflammation of the pancreas. The pain and nausea put them off their food. As cats obtain most of their fluids through their food rather than from what they drink they become dehydrated very quickly. The dehydration exacerbates the pain and nausea and so a vicious downward spiral continues.
Fortunately most respond to a drip to rehydrate them, and pain relief and anti-nausea medication. Within 2 or 3 days they are back to their normal selves.
Pancreatitis is a very common complaint in middle-aged to older cats. If your cat doesn't seem to be her or himself call us sooner rather than later as cats often suffer pancreatitis silently.