Cas shrugged. "I'm used to very little sleep in general," he admitted. "It's...become habit."
He didn't know whether or not to specify what it was he'd chosen to do with his time on Earth. For all he knew, this deity or being would perceive it as a threat and while Cas wished for a fight, his fight was not with the being before him.
"I would ask you the same, but if you are unable to sleep in general, that provides me with a more than accurate answer. You've...recently arrived, yes?"