When I start stressing myself out about all the things I need to do (before the world totally collapses, since I'm holding it all on my shoulders, ha!) I really activate my sympathetic nervous system (SNS). The spinal nerves that correlate with the SNS run from the area where the neck meets the back all the way down into the lumbar spine in the area of the hips. These nerves run from the spine into the chest and abdomen where they communicate with almost every organ of your entire being.
The activation of the SNS is often called the "fight or flight response," and we've all felt it when we've gotten an adrenaline rush. The overall effect of the SNS communication is that the blood flow is shunted away from 'unnecessary processes' and into the processes that can help us survive an immediate danger. The digestive organs, excretory organs (kidneys, large intestine), reproductive organs and some of the immune function is halted because those organs are no longer getting as much blood from the body.
Meanwhile, the heart, brain, lungs and muscle start getting a ton of energy so that they can go to work. The heart rate goes up and the conscious thought processes are increased. The pupils dilate, the bronchioles in the lungs dilate (more oxygen!) and sweat production is increased. We now have the power to run or fight to save ourselves.
What am I trying to save myself from? An overly long to-do? A self-induced overwhelm? Can I really run from the fact that I've spread myself too thin?
The problem here is that the tiger who is chasing me on a daily basis is an imaginary tiger that I created. (Though, on top of this, it could be a horrendous boss in a job I can't leave, or the stress of being a single parent, or any other forms of stuckness that occur as we are trying to survive and make enough money to pay the bills.)
At this point, when the SNS has been activated, I've got to do something for my body: I have to identify what the imaginary tiger is and deal with it before my "non-necessary" organs starve. In the case of a real tiger, it's worth a small stint in which I don't digest my food, give oxygen to my uterus or have a fully-functioning immune system because hey, I might die. Like. Right. Now. In this case of an imaginary tiger, this problem could go on for days, weeks, months or even years. And guess what happens when you starve your intestines, your ovaries and your lovely lymphatics of oxygen for that long....
When I think about the opposite of that fight or flight mechanism, I typically visualize an antelope. What are those beauties doing when they're not running from a tiger? They are ruminants and in good form, they are ruminating. They are getting messages through from the parasympathetic nervous system (PNS). This is the other side of the coin from the SNS and is often referred to as the "feed and breed" response.
The nerve fibers that correlate to the PNS extend into the body from the vertebra in the neck and from the triangular sacrum that sits at the end of the spine. The PNS stimulates digestion and excretory functions (urination, defecation) as well as increased production of saliva and tears and sexual arousal. It communicates to your body that your digestive, excretory and reproductive organs as well as your immune function so that they get the blood flow (and oxygen!) they need.
When a being is in a more PNS state, it looks and feels a little bit more like rumination. There is a deeper, more subconscious gesture to the thought process that is more meditative (as opposed to a state of cunning intellect.) The energy of the body is going to the excellent digestion of the food and digestive symptoms like gas, bloating and constipation are not huge problems. The libido is at a healthy level and the organs responsible for hormonal regulation of reproductive function, including the regularity of the menstrual cycle, have what they need to maintain homeostasis (a regular and healthy functioning of the body.)
We need both the SNS and PNS to live. These two sides of the autonomic nervous system are, in essence, the yin and yang of our internal communications network. One does not work without the other. However, it's important that we make sure we are spending an equal amount activating these systems so that we're not starving the precious parts of ourselves!