A good article about the discipline of moving away from our negative thoughts. This same author has written a related piece called The Science of Mindfulness, Part One: Cracking the Stress Response Code.
She focuses on the need to recognize the negative thoughts so that you can disassociate from it. While engaging in physical activity is a good way to break the cycle (doing yoga, going for a run), we can also “flip the switch” by being mindful of our negative thoughts. Once we realize that we are in a negative circle with thoughts, we can learn to move our thoughts systematically to other things that naturally make us curious and hold our attention.