Awareness of your stress symptoms can help you from becoming stressed. Now this sounds like a paradox, but the idea is that if you have sort of an early-warning system for stress, then you can start to deal with the issues that are actually causing your stress.
Persistent worry is an obvious signal of increasing stress levels. If your brain is constantly focused on problems or issues that need resolution, then you may be risking physical damage. During periods of high stress, worry may exclude all other thoughts and control your mind.