These things are very scary when they happen out of the blue, my other half has Crohn's which is largely asymptomatic but he suddenly became much more unwell and heart rate was through the roof and we called 999 and it turned out it was a perforated bowel caused by a ruptured appendix despite having had his appendix removed 50 odd years before but a bit had been left behind. Luckily he avoided surgery with antibiotics, steroids and a nutrient mix via a tube. A hospital stay of 3 weeks and oral steroids for 3 months. They did put him on some immunosuppressant meds but he could not tolerate them. But they took him off all meds for the Crohn's and he has only had one flare up since. He was apparently an unusual case and a first for the consultant.My partner has diverticulitis, the first we knew about it was eight years ago. He had been feeling off colour for a few days, then one morning he rang me at work saying he was in terrible pain. I went straight home and after seeing the state he was in, I called 999.
The paramedics gave him gas and air for the pain and carted him off to the hospital, after a scan they discovered his bowel had actually perforated due to an abscess bursting in one of the diverticula pockets, he needed emergency surgery.
So it can be very serious. Thank goodness he has been OK since, he's had a couple of small flare ups requiring a course of antibiotics, but nothing really bad.