Since I am not a mental health expert or a member of the military, it seems more relevant to feature the words of those who have experienced battle stress rather than make assumptions.  As I go through memoirs, I will post other accounts.

The Buna Campaign lasted three months (November 1942-January 1943).  In that campaign, casualty rates for combat units frequently were as high as 70%–and 30% loss is considered too stiff for troop cohesiveness and morale. 

In the Buna campaign, 2165 were killed; 3500 wounded; 15,575 treated for disease (jungle rot, malaria, dengue fever, dysentery were the major diseases).  Homer Wright served as a young officer with the 32nd Division in Buna and campaigns through the Phillippines.  He said:

Co. L & Co. M, 32nd Div, 128thThe battle fatigue we had was different from the World War I variety or what you saw in Europe.  The climate and disease wore out good men so fast.  We were tired beyond imagination.  The first impact was weight loss.  We were skeletons when we went back to Australia after Buna.  You couldn’t really sleep.  More like a fitful type of nap.  You were often interrupted.  We had guards out, but you had to be on alert at all times.    . . .
A good friend went through the phases of battle fatigue.  He never fully recovered from his jungle experience.  He was brave and a good officer.  But he was just worn out.  Beaten into the ground.  We were all tired of the war.  The 32nd was in combat through the Phillippines.  The number of people we saw massacred, both Japanese and Americans, gave all of us a bellyful of that particular phase of the war.  (Bergerud, 1996, p. 449)

In this chapter of Bergerud’s book, the stressors recounted for PTSD  (or battle fatigue, as they called it) were the discomfort of the tropical climate, but also the diseases that came with it.  Notable in these accounts is a lack of medical care personnel and medical supplies.  According to Costello (1981), the supply chain for the Pacific Theatre was particularly bad the first year: a lack of supplies and shipping assets, as well as logistical planning, was undeveloped. (318-323).

Jungle Rot, Vietnam Also the high attrition caused by disease created dissension between comrades: those who failed to take care of themselves were often seen as trying to take the easy way out.   Bergerud reports that a soldier who would stoically view the alarming disintegration of his feet from jungle rot could easily (and did) take exception to a soldier being mobilized out because of similar problems.  Some soldiers courted disaster, even by self-mutilation, in order to be relieved from this debilitating environment. 

Attrition also creates emotional gaps within survivors that affect the group morale.  For instance, newcomers into a high-casualty division were frequently not taken in by the group of veterans/survivors, who had already learned not to care for others strongly, lest they be overcome by still more personal loss.  Yet neither close attachment or its lack will obviate all survivor’s guilt. 

Further Reading:
Bergerud, E. (1996) and Costello, J. (1981) on Military Matters Library page.
32nd ‘Red Arrow’ Veteran Association web site: Part 3: The Papuan Campaign – Battle of Buna.  It’s interesting to note that the painting there depicts the consolation of grief as occurring among peers.