I have seen heads fall off as a reaction from a shock. If the polyp thinks its environment is going to kill it, it will drop the head off so it can be swept away to a better spot. Sadly I have done this to one or two small colonies in my tank because I cleaned the rock too much trying to get pest algae off. Just let that colony adjust as best it can, I doubt there is anything you can do to make it better. I would guess that after a little calm time in your tank, it will stop dropping heads. You can also grab those heads as they fall, or with a light brushing, some of them may fall off. Drill a small hole the size of the polyp in a piece of rock and stick the polyp in it. It will start a new colony there then. I have done that with very good success.