After a really really bad (prolonged) work situation, I started getting wicked acid reflux—with a very clear trigger between stress and subsequent symptoms. I remember at one point opening a passive-aggressive email from my boss and instantly feeling like a battery had exploded in my mouth.

The reflux never went away, even after my work situation improved, and some other gastrointestinal symptoms worsened until I recently got diagnosed with Crohn's disease. Which I am genetically predisposed towards, but I still like to say that my shitty boss gave me Crohn's (and not entirely in jest).

Although drugs have helped both issues immensely, I will say there's a pretty substantial link between my symptoms and bouts of stress. A lot of people with IBD (and to some extent, IBS) are all too aware of the paradox that if you spend too much time worrying about the possibility of a flare-up, you're all but guaranteed to have a flare-up. The tummy is a fickle beast!