About 18 months ago a number of things conspired against me: I was having a very stressful and uncertain time at work/home, and I went on a strong course of antibiotics for an infection which wiped out my gut (a known side effect). For about six months I had serious digestive problems, both bloating, gas, diarrhea, nausea, abdominal pain - real, visible, symptoms...but despite a barrage of tests, nothing at all medically wrong. I had dozens of blood tests, an ultrasound, a gastroscopy, and a colonoscopy with biopsies - nothing. At the same time, I went through a serious depression and malaise that nearly always coincided with my digestive problems.
A year an a half later, I have a lot more respect for how the gut is tied in to general mental health. I'm not totally back to normal, but I'm a lot better than I was, thanks to meditation, watching my diet (my gut is a lot more sensitive to what I put in now - previously, I would eat any old junk), and generally making that connection between my mood and my stomach.