Does gastritis or NSAIDS overuse cause diarrhea and all that good stuff?
It can. And sometimes it's not even from overuse. I found out many years ago that I can't take naproxen. A single pill gives me what I have described as "battery acid" diarrhea. Every. Single. Time. I refuse to ever take it again. Sorry for the TMI.
I've used many NSAIDs over the years, and naproxen is the only one that does this to me.
Of course, it could just be a bug.
Be sure to stay hydrated.