Sounds like perfectly normal behaviour to me. Corns will hide away while they digest and prefer to be active at dusk/night/dawn. You tend not to see much of them during the day. They'll also be more secretive as they work towards a shed.
If it's feeding time, then you can get him out to feed him. As Suzy says, he's unlikely to be brumating if the temps are correct and he's still eating.