I've had (what I assume is) IBS since my early 20s. It has got worse in the past few years and certain foods that I could tolerate before, I cannot anymore - onions and garlic particularly (used to be just raw, but now cooked ones too). I am rather lax about doing anything about physical symptoms and have only just started treating myself with peppermint oil (need enteric coated if you want to try, although not sure it's doing anything for me) and something you can buy over the counter called Kolanticon which contains an antispasmodic amongst other things. This seems to work, but unfortunately comes in a massive glass bottle, and my symptoms are often worst in the afternoons at work - I need to get round to decanting some. I have abdominal pain/discomfort, often on the left side (sidedness probably depends upon which part of the colon is sensitive), bloating, constipation etc. The worst symptom though is that my gut gets really noisy and it can sound almost like breaking wind, which is very embarrassing. Getting nervous about it inevitably makes symptoms worse.
I am sure that years of anxiety (particularly social anxiety) have sensitised my gut - I can feel even the slightest release of adrenaline as abdominal pain. Nowadays talking to people does not cause me mental anxiety, but my stomach still hurts - in fact I sometimes wonder if it is the only way that I know I am anxious about something now. When I was depressed I could also feel this strongly in my stomach and knew I was depressed even if I couldn't find any feeling of depression in my mind. I had no IBS when I was taking antidepressants and anxiolytics, although it is known that antidepressants can be an effective remedy for IBS independent of their anti-depressant effect. The gut contains neurons and uses the same neurotransmitters found in the brain, so it is no surprise that the two things are so closely connected.