I agree about the vet thing as well, I have 6 and all but 2 have been to the vet at one time or another...but, at the same time, I wonder why your tortoises were even out when it was 20 degrees outside or why it wasn't noticed that he was flipped earlier.

Maybe I'm just overprotective but anytime it gets down to 50 or below around here my tortoises are locked in their heated shed and checked on several times a night.