Hi Patricia,
Actually, epi's are different from Christmas Cactus. CC is the genus and species of Schlumbergera x buckleyi whereas Epiphyllums are hybrids of the genus of Epiphyllum. They are in the same family though and often grown in the same way.
I've not heard of a Christmas getting top heavy before. There might have been some rot going on in the stems, and that could cause it to break off at the base. Did it remain wet for any period of time? If it just broke from the sheer weight of the plant, then would repotting it to a bigger container help? I repotted mine last year before I gave it to my mother. Here is a pic below. If you are going to prune, you will want to prune after blooming and before new growth starts, which would be about now.
