Veiled, the question actually fits the options, being: "How Many Days in Succession Have You Had IBS?" Yes, IBS changes as you describe, though that is not being debated here. It is a clear question surrounding the symptom off IBS. The only option which is not present which I will add now you have questioned this, is the placebo factor, being "Do Not Have IBS."
If you have had it longer than 4 days in succession, then that is your answer. The other answers are there for personal choice only. I actually selected (3), because whilst I have been diagnosed in conjunction with my PTSD, IBS, I actually have not had IBS longer than a few days at once because it also factors not only on stress but diet. Yes, I could choose more than (4) because I have been diagnosed with it, but the symptom of IBS itself I do not suffer daily. You can be stressed all you like, but if your diet is actually quite good than you can avoid IBS at times.
I will add the placebo factor though now as your question did bring that to mind.