The Technical Explanation:As the stress response is triggered and the body's Sympathetic Nervous System (SNS) is activated, the adrenal glands release stress hormones like cortisol, while the Sympathetic-Adrenomedullary Axis (SAM) is also triggered to release catecholamines, which circulate through the bloodstream and the brain, and act on neuroreceptor cites to create changes in the body to mobilize energy, but create negative psychological and physical outcomes with prolonged exposure. Prolonged release of catecholamines can reduce the effects of certain neurotransmitters that affect mood, creating a negative feedback loop between emotions and physiology. These changes can also lead to chronic inflammation of organs and the failure of adaptive systems, which can lead to behavior and quality of life change, sleep disturbances and metabolic and cardiovascular disturbances.
These same catecholamines are part of the body's Parasympathetic Nervous System (PNS), or the relaxation response, which calms the body's physiology and returns the body to its pre-stressed state when the perceived threat is gone.
A More Simple Explanation:Catecholamines are an important part of the body's stress response, which can be vital but, if activated for too long, can produce negative health affects.
To counteract these negative effects, it's important to learn to return your body to its pre-stressed state before negative effects of prolonged stress set in. You can receive a steady stream of tips, research, discussions and other information by subscribing to the free weekly stress management newsletter.
Source: Sherman David K. et.al. (Sept 2009). Psychological vulnerability and stress: The effects of self-affirmation on sympathetic nervous system responses to naturalistic stressors. Health Psychology, Vol 28(5), 554-562.