Log what came up and when: undigested food soon after eating, an occasional hairball with fluid worth watching, and yellow-green bile or blood raising concern.
A single vomit with normal energy and appetite can be managed with a short food pause and small frequent water, but kittens and sick cats should not fast long; call the vet instead.
Repeated vomiting beyond a day, diarrhea with fever and dullness, suspected string or foreign-body ingestion, and a painful abdomen all call for prompt veterinary care.
Bring photos, frequency notes, and recent diet changes to the visit, and never give human anti-nausea drugs, whose doses and ingredients can go wrong.
