In the future, (and I hope this never happens to you again,) you can go ahead and put the screw into the hole in the pipe that you accidentally drilled and it will plug most of the flow of water and give you time to get to the shutoff with much less water damage.

I imagine you will always drill carefully and stop at the drywall and use a probe to check what's inside from now on though. Something like this sticks with you.