The same can be said for PTSD. Whether or not chronic stress leads to hypocortisolism and burnout/CFS seems to be whether or not dealing with the stress is in the best interests of the organism (https://www.ncbi.nlm.nih.gov/pubmed/15950390), along with other factors such as time since onset, nature of the stress, personality factors, etc.

Stress-related disorders are quite common among the military and refugees (higher level of prevalence than the general population).