[header] How to help a vomiting cat [title] Note any changes to your cat's diet, thirst or behavior. [step] To determine why your cat is vomiting, think about changes to your cat's diet, thirst, and behavior. Start by remembering when and what your cat ate last. 
Note if your cat is drinking more or less than usual. Also, check the litter box to see how often it has been used and if the cat has diarrhea.