The parasympathetic nervous system is not often thought of but extremely important. One has often heard of the Sympathetic Nervous System also more commonly known as the "fight or flight" system1. Therefore the Parasympathetic Nervous System can be remembered as the opposite of the fight or flight response and instead as "rest and digest"1.
When one is in danger you want your Sympathetic Nervous System to help you respond appropriately such as if you are being charged by a tiger. However if you are in traffic and someone cuts you off your Sympathetic Nervous System can also start up. The more important thing is that once the danger subsides your sympathetic response should also stop and your parasympathetic nervous system should kick in and you can go into rest and digest mode again.
The nerve fibres of the parasympathetic nervous system are the cranial nerves, primarily the vagus nerve3,4, and the lumbar spinal nerves. When stimulated, these nerves increase digestive secretions and reduce the heartbeat1.
The problem with society today is that many of us are living in the Sympathetic Response constantly and not returning back to the parasympathetics1. Interestingly there are specific things one can do to try and return back to a parasympathetic response versus a sympathetic one including a chiropractic specific adjustment2. Diastolic pressure (indicating a sympathetic response) dropped significantly post adjustment among those receiving cervical adjustments, accompanied by a moderate clinical effect (0.50) and it is preliminarily suggested that cervical adjustments may help result in parasympathetic responses2. Yoga, deep breathing and meditation can also help you shift to a more parasympathetic (healing) state.