Any coral is can go throw phases of inactivity, even ones as hardy as favias. Keep an eye on it, as long as it is not in crazy high flow it's position regarding light is fine. In fact sometimes I think we have a tendency to love these things to death by continously moving them around trying to make the coral happy. Just go through a quick checklist- moderate light and current, no offensive neighbors, params in check, if these are all fine just leave it alone. The prism favia in my avatar was "rescued" from a failing LFS and it's had a tough past year. When it was placed in my tank it started really looking good until I had to transfer everything to a larger system. Even though the params in the new tank were the same or more stable than the previous this favia took the move real hard. It looked very crappy for a month or so and now it is really start to come back- sometimes this is just the way it goes. I guess if they liked being moved around they would have evolved legs.
Plus remember one other thing- sometimes regardless of the finest care we provide, stuff just fails- it's a sad crappy part of the science of reefing...