Ya know, the worst thing that could happen with the hypno CDs is that they don't make a huge change in your IBS, but you get some extra napping time in. Honestly, all it involves is relaxing for half an hour a day while you listen to some music and a guy speaking very calmly.
The hypno CDs did teach me how to turn off my anxiety, but the learning was gradual to the point of being imperceptable. I found it the most useful when all I expected from it was a relaxing time to close my eyes (which is very nice, and does help with the IBS since fatigue is a huge trigger).