Your ANS is that part of the nervous system which functions to sustain your life by helping to control your heart, lungs, digestive system, blood pressure, immune system, certain reflexes; such as coughing and gagging, fluid balance, pupil diameter, sweating and sexual function. There are two branches of this system. The sympathetic branch is more in control when you are stressed, nervous, or excited. The parasympathetic branch is more in control when you are sleeping, relaxing, or recovering from an illness or injury.
A balance between the two branches is essential for good health. In fact, most illnesses and injuries cause or result from an imbalance between those two branches. An imbalance in your ANS can tell your doctor many things about how healthy you are as well as what can be done to keep you healthy as possible.