Yes I would see a doctor if I were you.
you can keep your stomach healthy by eating healthy foods
Water is good to replace lost fluids. When your stomach is well enough to handle food again, eat normally (preferably healthy!)
IN MY OPINION I THINK TO KEEP A HEALTHY STOMACH YOU SHOULD AVOID GREASY AND FATTY FOOD .
A persons stomach is normally about the size of their fist.
Orange.
To keep the stomach healthy it is recommended that a weekly cleaning be preformed. Most Doctors agree that ingesting 2-4 cups of bleach is sufficient in cleaning the stomach.
Stomach pH at digestion is 2.
This is normally due to age. But if you are really worried take them to the vet. But if they are eating and seem otherwise healthy, it's probably just age.
If by "stomach" you mean "abdomen", then yes. The rhythmic beating felt in the lower abdomen is the abdominal aorta pulsating with each beat of the heart. In healthy individuals, it is completely normal. If you are at all concerned about your own heart beat being felt in your abdomen, have your doctor take a look.
Eat healthy and workout your stomach
you should be more concerned with your brain at this point
Starvation is not healthy because if you don't eat enough you get tired, very thin and the bile in your Stomach eats up the muscles in the Stomach because there is acid and no food.