I have held in D before. Just seems to make my D for that day worse when I finally release it.
I don't think you can really, permanently damage yourself doing that--else I would be damaged because I've held back bowel movements (D and normal) plenty of times (used to have a phobia about pooping in a public restroom).
It could be that you have IBS-A, which is IBS that alternates between D and C. There are a number of people on here with that problem, and they can altnerate every day or two, or switch only after having months of one kind. And some people with IBS start out having one type and then switch, for no apparent reason, to the other type and are like that for years.