Just to put a finer point on it, I don't think you can "shut down" your mind. That's a bit like trying to achieve a negative, so to speak: "Don't think about pink elephants." The first thing your mind will do is think of pink elephants. But you can quiet your mind by filling (not emptying) it with simple focus, such as the illustration I posted earlier suggests. In this way, the thoughts that give you stress will take a back seat; you'll be able to observe them from a greater distance when they arise, you won't attach to them, they will be more muted, and then they will dissolve. And so it goes.