The nervous system is divided into many sections with a variety of functions. One section of the nervous system is the autonomic nervous system. The autonomic nervous system controls bodily functions such as heart rate, respiratory rate, digestion and pupillary response. The autonomic nervous system is then divided into two more sections, the sympathetic and the parasympathetic nervous systems. Each division enables the opposite functions. The sympathetic system arouses your body causing your heart rate to increase, your respiratory rate to increase, your digestion to slow down and your pupils to dilate. The parasympathetic nervous system does the opposite to all of the bodily functions.
When I was younger, I had an extreme fear of any medical facility, which is ironic considering I am now in nursing. I would avoid going to all medical appoints. When my mom would make me go to the doctor I would burst into tears and beg her not to make me go. One day I had to go to the hospital with my mom for her to drop off a sample, she convinced me I would be fine because I was not going to be a patient. All I had to do was walk to a desk, drop off the sample and go back home, seemed simple enough. This small task caused me such distress that when I was walking to the desk my sympathetic nervous system started to engage. My palms were sweating and my heart was racing. When I finally got to the desk the nurse asked me my name but I could not respond, I tried to hand her the sample but the next thing I knew I was on the ground. I fainted and fell straight to the floor. This small task of going to the hospital, caused fear to take over my body and my parasympathetic nervous system to overcompensate for the situation I was in. To help me calm down my parasympathetic nervous system lowered my heart rate, slowed my breathing and caused the blood vessels in my legs to dilate causing blood to pool in my legs. My parasympathetic nervous system slowed my down my bodily functions to such a degree that there was a lack of oxygen in my brain which caused me to faint. Luckily, I was in a hospital so almost everyone around me was qualified to help me increase my heart and respiratory rates back to normal levels.
Most people consider your autonomic nervous system the “fight or flight” response, what they fail to explain that there is also a freeze section of that system. Sometimes when the level of stress you are in is too overwhelming, you freeze because your parasympathetic system takes over for your sympathetic system.
https://medicalxpress.com/news/2019-06-people-faint.html#targetText=The%20body%20reflexively%20compensates%20by,oxygen%20%E2%80%A6%20and%20you%20lose%20consciousness.