The rain of blows does not affect Castiel so much as the snarl of emotions that seems to be driving them.

Castiel does not even know where to begin going about untangling it.

And he is worried that Dean is going to do damage to himself in this state.

So it is for his benefit rather than his own that Castiel reaches past the flailing fists and rests two fingers against Dean's forehead.

Willing him to sleep.