It could happen for various reasons. Your kitty may have developed a tummy ache from slurping that bit of milk you just offered after having breakfast or he or she may have internal parasites. It could also be she cannot tolerate that new cat food you just brought her or simply she just eats too fast. Hairballs are notorious causes of vomiting and it cannot be repeated enough that in some cases, vomiting may also be indicative of serious issues. Serious issues such as intestinal obstructions, kidney disease and even cancer.

Home Remedies for Upset Stomach in Cats

-Fast 

When the stomach is upset nothing help more than giving it some rest. This is what a cat does in nature: he loses his appetite for a few hours and eats only until feeling better. In domesticated cats however, canned or dry food left out may be too enticing with all the stuff they are filled with to make them extremely appetible. Therefore, it is best to simply pick up all cat food and put it away for a 12 to 24 hours fast. While adult cats can fast for up to 24 hours, small kittens however, should not be fasted for so long, usually a overnight fast should suffix.

-Hydration Check

If the cat has vomiting or diarrhea or both, he may be losing a lot of fluids. A good way to monitor a cat's hydration level is to pull up the skin over the shoulder in a tent and see how quickly it springs back into position. In a well hydrated cat the skin will spring back immediately, whereas, in a dehydrated cat it will have a delay or worse, the skin will remain lifted. In such cases, the cat is critical and will likely require some fluids administered from the vet.

-Fluids

Fluids must be given carefully. In some cases, drinking water may cause a cat with an upset stomach to vomit, further dehydrating him. Ice chips that can be licked may help. Unflavored Pedialyte may be dropper fed very slowly to cats that are at risk of becoming dehydrated. However, a cat that cannot hold water should be seen by a vet because of the risk of dehydration.

-Bland diet

After the 12-24 hour fast cats with upset tummies should be put on a bland diet. This may consist either of:

Option 1) Some well cooked white rice with skinless and boneless chicken or boiled hamburger with the grease drained off. This food should have more rice than meat and it should be offered in small quantities throughout the day. 

Option 2) Some meat based baby food with no onion or garlic listed in the ingredients. This baby food may be diluted with some water to encourage food intake. Warming it up at a safe temperature may encourage cats that have no interest in food to eat.

-Stimulate Appetite

Cats that are not interested in food may be enticed to eat if they smell some good food cooking. Try to  boil some chicken or fish and often, your cat will sniff the aroma getting hungry. If this does not work, try warming up the food a bit. Cats that do not eat for more than 1-2 days may risk a serious condition known as ''fatty liver disease'', therefore, it is important that they eat something even if these may mean force feeding at times. Veterinarians often may prescribe appetite stimulants to cats that lack appetite. A product called ''Nutrical''  available at pet stores, can be given to provide some temporary caloric support.

-Energy Boost

If the cat is not diabetic, rubbing some pancake syrup on the gums may give a little boost of energy. This is a good time to check the gums and make sure they are still the nice pink color they are supposed to be. If the gums appear pale, whitish, grayish or anything other than healthy pink, it is important to have the cat seen immediately.

-Hariball Remedies

If the vomiting is due to hairballs, products such as Laxatone may be helpful. As an alternative, just a little bit of vaseline may be put on the cat's paw to  be licked off. Other options are to use some oil from a can of tuna fish, some plain canned pumpkin with no spices added (not pie mix), or a little bit of butter.

-After a While

Once the cat is no longer vomiting and the stools are better formed,  the regular diet the cat was on may be re-introduced gradually in 3-4 days.Refrianing from doing so and adding the normal diet too abruptly may cause a cat to go back to vomiting and having diarrhea..

-Practice Caution

While Home remedies can help cats overcome a mild stomach ache, a cat that has lost appetite, appears sluggish or in pain, that vomits very frequently or has uncontrollable diarrhea with a lot of fluid loss, should be seen by a veterinarian. There may be some underlying causes that needs taken care of at times and this cannot be accomplished at home.

Disclaimer: the above article is not to be used as a substitute for professional veterinary advice. If your cat is sick, please refer to your veterinarian for a hands on examination and professional advice.