Appendicitis occurs when your appendix, a worm-shaped pouch attached to the large intestine, becomes inflamed.
It can be life threatening if the appendix bursts, but doctors usually remove it surgically before this happens.
A diagnosis can be tricky, however, says Michael Payne, MD, a gastroenterologist with Cambridge Health Alliance, a Harvard-affiliated public healthcare system, in Cambridge, Mass. "It is a very common illness and many people don't have classic symptoms," he says. "We actually have to put our hands on a belly to see for sure."