The Fresnel Lens is top heavy, I would move it to the bottom shelf so if it happens again at least you don't run the risk of it breaking the shelf if it falls over again.
Or if you have something you can run a fishing line around above it on a shelf above or the top of the case you might try that possibly a small eye hook in the top of the case if it's wood with a piece of clear fishing line run thru the brass to keep it in place.