My worst experience ever in my whole life occured while I was in France. If I recall correctly, I was staying in a coastal town, although I can't remember what it was called. Anyway, after a few days there, all seemed well (other than the obvious hindrances of not being able to speak the national langauge and being treated as a second-class citizen for it).
About 3 days in, I sat down to watch episode 2 of the BBC series Sherlock on TV, although the reception was terrible as it was being broadcast from another country. I just about made out what happened most of the time, and the audio was clear enough, so I was satisfied enough as the episode came to a close. I decided to get some sleep afterwards.
After a while, I realized I couldn't get to sleep. I had a mild discomfort in my belly, which worsened as time went on. It got to the point in which it was incredibly uncomfortable and I had to get out of bed and into the bathroom. I sat on the toilet for a while, presuming that I was just constipated. But nothing came out the rear end.
I finally gave up and got off the toilet, when suddenly, out of nowhere, I threw up onto the floor. I sat back down immedietly and it all started to flow out my rear. An endless stream of liquid feces filled up the toilet. I started to throw up at the same time.
This literally did not stop for the rest of my stay. For about 3 or 4 days, I spent most of my time sitting on a toilet, throwing up into a bucket whilst brown liquid streamed out my anus. It was not pleasant.
I prayed for it to cease, but it didn't look like it was going to stop. I was forced to book a ferry back to England a whopping 1 day early. I was due to leave on a Friday, and, ironically, everything stopped the moment I woke up on Friday. No more sickness, no more diarrhea. I was thankful the experience was over, and I got out of France as soon as I could. I haven't visited since.