If you were enjoying a day in the garden you are in a parasympathetic state (relaxed). However, should a hungry tiger jump over the wall and walk towards you will switch to a sympathetic response: muscles engage, blood vessels constrict, pupils dilate, and heart rate will increase so you can hastily get away. Once in assured safety your will return to a parasympathetic state.
When the sympathetic response is being triggered too frequently or continuously the balance of this evolutionary-driven system is thrown out of whack, and negative effects occur.
Continuous stress from a perceived negative situation or physiological source causes a sustained low-grade inflammatory response which has catastrophic effects on the body. Symptoms of aching joints, poor sleep, fatigue and, mood and behaviour changes may take place. If this continues it may affect the immune system, making us more susceptible to infections; damage the gastrointestinal tract, causing digestive disturbances; increase the risk of Alzheimer’s disease and heart disease, as well as increase depressive and anxiety disorders.