Elizabeth Svoboda was just 15 years old when she developed bouts of gnawing pain in her lower belly so bad, she would have to lie in the fetal position for hours until it subsided. Every few weeks, and for the next 2 decades, the sensation would return, disabling her.

“I’ve been through labor, and I would say that at its worst, my pain was comparable to that,” said Svoboda, now 42, of California. It wasn’t until college that she addressed her pain with a doctor who, without doing any tests or imaging, ultimately chalked it up to irritable bowel syndrome (IBS): an intestinal disorder known for causing belly pain, gas, diarrhea, and constipation. “At that point, I sort of threw up my hands and said to myself, ‘Nobody is going to be able to figure this out,’” Svoboda said. “I just accepted that this was my normal state of being.”

Little did she know, it would take nearly 20 years of pain to figure out what plagued her: chronic appendicitis. Although no official definition exists, a person is thought to have the condition when their appendix, that finger-like pouch at the end of your colon, becomes inflamed and causes belly pain in regular on-and-off episodes that can span weeks, months, or years. Chronic appendicitis is rare, according to current estimates. Studies have found that it occurs in about 1% of all cases of appendicitis, and affects adults and children alike. Appendicitis is almost always acute, meaning it strikes suddenly and worsens quickly, sending people into emergency surgery to remove the organ. It occurs in 7% of the U.S. population, with 250,000 cases reported annually; most are diagnosed in people between 10 and 30 years old, but anyone can have it.

Both chronic and acute versions of the condition cause similar symptoms: pain that begins around the belly button and eventually moves to the lower right side of the belly, as well as nausea, vomiting, fever, and loss of appetite. The main difference between the two is timing, said Reezwana Chowdhury, MD, a gastroenterologist and assistant professor of medicine at Johns Hopkins Medicine in Baltimore. Acute appendicitis typically comes on within 24 to 48 hours, while chronic appendicitis can come in episodes that last several hours and reappear randomly for at least a week, but usually more.