"Physiological Exhaustion" comes next, let's just summarize it with a short quote:
Psychologist F. C. Bartlett emphasized the psychological impact of physical exhaustion in combat. "In war," he wrote, "there is perhaps no general condition which is more likely to produce a large crop of nervous and mental disorders than a state of prolonged and great fatigue." The four factors of (1) physiological arousal caused by the stress of existing in what is commonly understood as a continual fight-or-flight-arousal condition, (2) cumulative loss of sleep, (3) the reduction in caloric intake, and (4) the toll of the elements — such as rain, cold, heat, and dark of night — assaulting the soldier all combine to form the "state of prolonged and great fatigue" that is the Weight of Exhaustion.

Next: Horror.
Beyond fear and exhaustion is a sea of horror that surrounds the soldier and assails his every sense.
Hear the pitiful screams of the wounded and dying. Smell the butcher-house smells of feces, blood, burned flesh, and rotting decay, which combine into the awful stench of death. Feel the shudder of the ground as the very earth groans at the abuse of artillery and explosives, and feel the last shiver of life and the flow of warm blood as friends die in your arms. Taste the salt of blood and tears as you hold a dear friend in mutual grieving, and you do not know or care if it is the salt of your tears or his.