My mother has it. Has for YEARS.
It's when the pockets in the intestines get food stuck in them and get infected. You'll usually have abdominal pain, nausea, diarrhea and a fever. Most times you need antibiotics to clear it up and to avoid your trigger foods....nuts, seedy fruits and veggies, corn, strawberries, etc.....everyone is different and triggers and symptoms vary.
She gets it several times a year because she's VERY non compliant with her diet. And she has scarring in the bowel that with the next bout or 2 they may have to remove the damaged part and leave her with a temporary colostomy. I've been b!tching for years at her to try to get her to change her ways.