Therefore, while the PNS is doing its job to bring about a gradual state of relaxation, it may take a while for some of those anxious feelings and physical sensations to go away. These sensations may include: dizziness, lightheadedness, chest pain, racing heart, tingling sensations, breathing difficulty, nausea, upset stomach or stomach pain, dry mouth, constipation, and perspiration. These anxiety symptoms are created by the activation of the sympathetic nervous system in preparation for fight-or-flight. These symptoms occur as the nervous system activates the other body systems to perform well during a fight-or-flight situation. Now let's examine how these symptoms occur:
The cardiovascular system: During fight-or flight, the body requires additional oxygen to fuel the muscles. Therefore, the heart must beat faster to pump more blood. The blood supplies the oxygen. The anxiety symptoms that people describe include feeling as if their hearts are pounding out of their chests, or feeling as though they are having a heart attack. However, there are certain parts of the body that need more oxygen than others do. The body is very fuel- efficient. Therefore, it reacts by restricting blood flow to areas that do not need it as much (like your fingertips and toes). Blood flow is re-directed to areas where it is needed the most (like the large muscles in your arms and legs). Because of these actions, our extremities can become cold, or feel tingly. This is because they are not getting the usual amount of blood flow.
While your thighs and biceps are getting more blood flow than usual, your brain is getting a little less. This may seem alarming. However, during fight-or-flight, your brain's ability to think is not nearly as important as your heart and other muscles working well. After all, you are not trying to solve a problem. Rest assured, this temporary decrease of blood flow to the brain is not at all harmful. Nor will it cause any long-lasting harmful effects. However, it does cause temporary symptoms such as dizziness or lightheadedness, or feelings of unreality. It can also cause temporary memory problems, and difficulty with concentration.
The respiratory system: Since the heart is working harder to increase blood flow to carry more oxygen, the respiratory system must do its part by working harder to increase the amount of available oxygen. Respiration must increase. The additional oxygen provides the necessary energy to fuel the muscle cells. The increased respiration gets extra energy to those muscles fast! It produces a feeling of being out-of-breath, or being unable to get enough air. It can also cause tightness in the chest, and contributes to feelings of lightheadedness.
The excretory system: In addition to increasing respiration and heart rate, the SNS also causes the body to perspire. Believe it or not, perspiration has several very protective functions. First and foremost, it operates as the body's air conditioning system. It cools the body down so that it does not overheat. The by-product of muscles working very hard (including the heart muscle) is the generation of heat. Perspiration allows this additional heat to dissipate. Additionally, it makes people more slippery. That may sound gross, but if you are in a fight and someone is trying to grab onto you, the additional perspiration due to the SNS activation can make it more difficult for your attacker to grab you and hold onto you.
The digestive system: While the SNS generally turns things "on" there are some exceptions. The digestive system is one such exception. The body is very fuel-efficient. In order to conserve "fuel," it shuts-down unnecessary bodily functions, while it is in a high-alert state. It turns out that digestion is not a particularly necessary function during these high-alert moments. Remember, "Man your battles stations!"? We can hardly picture a soldier eating a snack while doing so! Thus, a system that turns "off" during fight-or-flight is the digestive system. Instead, the digestive system is one of the systems that is turned "on" by the parasympathetic nervous system (the rest-and-relaxation system). An easy way to remember this is by thinking about how you feel after a Thanksgiving Day feast. What do people tend to do? Sit down and relax, or take a nap. This allows your body's efforts to be focused on digesting that big meal.
When the digestive system has been "turned off" due to SNS activation, many gastrointestinal symptoms may occur. People may experience feelings of nausea or stomach pains. In addition, you can experience a dry mouth because the production of saliva also serves a digestive function. Because of the slowing of digestion, constipation can also result.
As is evident from the above discussion, the activation of the SNS makes the whole body work harder. This can lead to aftereffects such as a feeling of exhaustion. It is like running a marathon without actually running. Outwardly, your body may not look like it is working that hard. However, on the inside, the SNS activation expends a great deal of the body's fuel and the result is extreme fatigue.