On Killing by LtCol Dave Grossman, 2009, Excerpts
To understand the intensity of the body’s physiological response to the stress of combat we must comprehend the mobilization of resources caused by the body’s sympathetic nervous system. In combat this very often results in nonessential activities such as digestion, bladder control and sphincter control being completely shut down. This process is so intense that soldiers very often suffer stress diarrhea, and it not at all uncommon for them to urinate and defecate in their pants as the body literally “blows it ballast” in an attempt to provide all the energy resources required to ensure its survival. As soon as the danger and the excitement is over, an incredibly powerful weariness and sleepiness backlash occurs on the part of the soldier.
In continuous combat, the soldier roller-coasters through seemingly endless surges of adrenaline and subsequent backlashes. Unable to flee and unable to overcome the danger through a brief burst of fighting, posturing, or submission, the bodies of modern soldiers quickly exhaust their capacity to energize and they slide into a state of profound physical and emotional exhaustion. A soldier in this state will inevitably collapse from nervous exhaustion – the body simply will burn out. The lack of sleep, lack of food, the impact of the elements, and emotional exhaustion caused by constant fight-or-flight-response activation all conspire to contribute to the soldier’s exhaustion.