It's because we arent made to nap in the day. You mess up your sleep routine and it acffects your tummy. Try not to fall asleep when u rest in the day
You never have this pain when you wake up from sleeping at night? Only when you take naps? Do you sleep in a different spot when you take your naps, like perhaps on the couch instead of your bed. Maybe your body is more cramped if you're not in your bed. You may just start out by seeing your family doctor. Even if you haven't eaten for a couple of hours your body may still not have had the proper time to digest your food. Also, if you exercise after you eat before your nap your body does not digest during exercise which is why you shouldn't exercise on a full tummy. It could also have to do with a medication you take during the day. There are a lot of possibilities...try your family doctor first and he/she may refer you to a gastrointerologist. Good luck!