I don't know what causes this pain or if it is always related to IBS but I do occasionally get those sharp stabbing pains too ... really is agony!!! Often to the point I can't stand or sit! Sometimes they come before a bowel movement or if I am having an IBS -C spell. Usually they ease up after a minute or two.
Does any of this sound familiar?
Incidently, my mum also gets these pains from time to time ... she has no history of IBS. But the pain can also be an indicator of haemerroids. The first time I got those pains she told me to stand on my toes and that would ease them away! It actually works too, on the occasions I can manage to do it without falling about laughing!