What is indigestion or overeating?

The human stomach can hold approximately one liter of food. If you overeat more than most people do, your stomach expands to accommodate up to four liters of food. When the stomach expands to accommodate this additional volume of food and drinks, you feel bloated and may experience stomach discomfort.
When the stomach expands, it is pushed against your diaphragm, causing a sensation of shortness of breath or interfering with breathing.

Pain in the upper or lower abdomen, nausea, gas pains, belching, and bloating are symptoms that can occur due to overeating.

Because the volume of food and drink in your stomach is too much, your stomach starts to produce more acid to help digest the food. This excess acid production can relax or weaken the lower esophageal sphincter, which is a tight band of muscles at the bottom of the stomach that prevents food from flowing back into the throat. If the lower esophageal sphincter fails to work properly, stomach acid begins to travel up the esophagus (the tube that connects your mouth to the stomach).