I did some Internet searches with respect to frilled dragons and hibernation.

It appears that frilled dragons can hibernate.

If you are concerned, to be on the safe side, try for a temporary in-expensive space heater to raise the temperature above 60 degrees this should assist digestion and encourage eating.

A metropolitan herpetology article referred to burmation for breeding purposes.

It came with the warning that:
"....if during the time they are hibernating you start to see one of the animals losing an extreme amount of weight [which shouldn't happen if the temperature is low enough], separate that animal and provide some food and water. It may not finish it's brumation, but it's better to have a healthy animal to breed next season then to loose it from dehydration or malnutrition)"

http://www.metroherpsociety.org/care-sheets/frilled-dragon-chlamydosaurus-kingii.php

best wishes