My wife and I visited Mexico in 2006 with 4 of our friends. It was an incredible trip, everyone had a blast. We managed to avoid any gastrointestinal issues right up until the very last day, when all 6 of us came down with various degrees of the same symptoms (nausea, cold sweats, diarrhea). We stayed and ate on the resort up until the last day. Near as we can figure, we narrowed down the culprit to 2 possibilities.
On the last day, we visited Chitzen Itza. On the way back, we made 2 stops. First, we stopped at a cenote and went for a swim. It's possible that some sort of bacteria in the water made us all sick. Then, we stopped at a small town on the way back to Playa del Carmen, and visited a market, and had an "authentic" Mexican lunch at a food court in an open-air mall.
I know reading this, it seems obvious that it was the food. But we all had different things for lunch, and some of us barely ate at all. The only common demoninator we can find was the swim in the cenote. At any rate, both experiences were amazing, and we'd do them again anyway, even if we knew it meant a few hours in the bathroom. The memories will stay with us forever.
