Castiel doesn't frown much, but the look he shoots Sam is certainly calculating.

"Is he prone to overworking himself?"

Off to their side, Dean is making a whipping gesture silently, and Castiel doesn't really care. He can't have Sam overworking himself - not if they're to ever stand a chance of getting Castiel with child. They'll both have to be in peak condition physically and mentally.

So yes, if need be - Castiel will physically drag him away from his work.