Yes, I know the feeling, "want[ing] to silence [your] brain and [you] can't".

I think the problem is twofold: first there's the anxiety which creates unwanted thoughts and second there is the obsessive desire to be able to control one's own thoughts, to silence them at will.

In any case, getting up and doing something, getting outside of one's own thoughts, that is the practical solution which has been supplied here adequately. I don't think there is a permanent solution even after medication and therapy, we have to learn to have patience for our own anxiety.