What helps me if I'm feeling really overwhelmed and anxious is setting dedicated worry time. It's an exercise my therapist taught me when I was in the grip of major depression and a few anxiety disorders. Takincareome touches on this above.
I allow myself 15-30 minutes a day to worry and fret and bounce crap around my skull. Outside of this time, I have to let things go. I feel safer knowing I can revisit the worry in a controlled way at a later date. It's an internal boundary which I've found really useful.