Based upon the work of Dr. Hans Selye and other physicians who have studied the physiological response to stress, we now know that much of the immune system is involved in the stress response. An example to which most of us can relate is the tendency to get a cold during a period of stress or after a long period of physical exertion.
The immune system of the body can be viewed as an army of small soldiers of cells that are able to conduct physical combat and chemical warfare. Dr. Wayne Hodges of the Savannah Pain Clinic in Savannah, Georgia, has described the immune system as, "An army of cells which actually smother and take hold of harmful organisms which enter the body system. They are capable of literally squirting chemicals that kill organisms and communicate to other body organs to make certain defenses against disease and illness."
During long periods of stress and unrest, the body's immune system becomes impaired or, at least, compromised. The exact reasons are rather technical but are primarily a result of increased levels of catecholamines which begin to impair the response of the immune system. The important thing for us to know is that frequently illness is brought on as a direct result of poor rest habits and long periods of stress. One who rests well will usually do better at resisting some types of illnesses.