Castiel is back in his hide since yesterday morning, he hasn't eaten though, so I was ok with it. I checked this am, he opened his eyes, not sure if he's sleeping, will give him 1 more day, if he's still awake, I'll get him on his basking spot.
You can try not feeding him, even if he sleeps, he'll needs to do a last poop to get his digestive system empty. If he's like Imp and just wants to sleep for a few days, let him. Remove the food, turn the lights off and let him sleep. I never let Imp sleep for more than a week if he's not done his last poop. Give it a try, see what happens. If he doesn't sleep after 2 days, haul him out, put lights back on and see what he does. Some just don't get the hang of brumation.