I have found that when you tell anyone you have IBS they just assume you have the occasional stomach ache - they have no idea how serious it can be or how much it rules your life.
It affects me every day, pretty much all day, but if I mention it to friends they say something like "I`m sorry you`re having a bad day". I wish it was called a "disease" - I think it would then be taken more seriously. There are times when I have been tempted to lie and say I have Chrones Disease. People might then understand my need to be near to a loo and the fact that I feel unwell most of the time