Your autonomic nervous system (ANS) is the part of your nervous system that functions to sustain your life by controlling your heart, lungs, digestive system, blood pressure, immune system, certain of your reflexes, fluid balance, pupil diameter, sweating, and sexual function.

Your ANS has two parts.

There are two parts (or branches) of your ANS:  the sympathetic branch and the parasympathetic branch.  Generally, the sympathetic branch is more in control when you are stressed, ill, or injured, while the parasympathetic branch is more in control when you are relaxing, sleeping, or recovering from an illness or injury.

A balance between the two branches of your ANS is essential for good health.

In fact, most illnesses and injuries cause or result from an imbalance between these 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 as healthy as possible.