I started having symptoms of colitis ulcerosa when I was 18 and had final high school exams. I was under tons of stress. I started to care much less about such things and had years-long remission. There were only 2 other flare-ups - when I was passing driving licence test, and when I had the first big series of exams at university.
Basically every time I drove myself very hard I had another episode. And it's not fun to suddenly shit yourself in public transport let me tell you :/
It's been over 20 years since last time I had colitis ulcerosa flare-up. But, in the meantime I was also diagnosed with autoimmune liver disease (PSC), and I'm not sure this one is stress-related. It seems to me it just ticks away at my liver and even very relaxed lifestyle doesn't help. I'm very hopeful about new drugs for this, as the only alternative seems to be to wait for inevitable liver transplant later in life.