Taking time every day to promote parasympathetic activity is an absolute necessity if one desires good health. The best way to achieve this is to participate in some type of mindful activity that encourages relaxation. Yoga, Tai Chi, Qi Gong, Meditation or even just 5-10 minutes of deep breathing are some of the best ways to achieve a parasympathetic state. There are several biofeedback tools that can be used with a home based PC that also work to get the nervous system into a parasympathetic state.
The beauty of these exercises is that you do not have to do them for long periods of time to get significant benefits. In the same way that a sympathetic trigger (slamming the brakes to avoid a fender bender) will cause effects for hour after the event is over, a parasympathetic trigger, like yoga class, will also cause positive effects on your body for several hours afterwards.
In addition, the more you engage in parasympathetic training by doing these sort of exercises the easier it is for your body to relax after a stressful event. Your conscious connection for activating parasympathetic activity becomes stronger and when you start to get stressed your brain will have the power and training to automatically shift into relaxation mode. It is well known that individuals who engage in daily relaxation practices have a much better capacity to handle stress and are less likely to suffer from many diseases made worse from stress like heart disease, high blood pressure, diabetes and even cancer.