I am not sure about frogspawn, but since it is very simular to a hammer, I would say the feelers will start to disappear, not small, but kind of mushy then gone. and the body which is a skeliton type will be easly seen,
My hammer did that once, it may be stressed. Did you check your water, alk, calcuim, ph, if your alk get to low, it can kill your coral quickly.