In order to discuss if the three scenarios are actual instances of abnormal behavior and if is should have a diagnosis, one has to be able to recognize the presence of disorders. Some mental disorders exhibit several psychotic symptoms, and other disorders are more subtle variations on normal experience. Most mental disorders are typically defined by a set of characteristic features; one symptom by itself is seldom sufficient to make a diagnosis. Each symptom is taken to be a fallible, or imperfect, indicator of the presence of the disorder. The significance of any specific features depends on whether the person also exhibits additional behaviors that are important. Many unusual behaviors and inexplicable experiences are short lived; if we ignore them, they go away, but some forms of problematic behavior are not transient and they eventually interfere with the person's social and occupational functioning.
Looking at the first scenario with the young solider back from Iraq, who is experiencing some symptoms similar to a depressed mood to possibly clinical depression. The soldier has difficulty sleeping because of nightmares, consumed with guilt of killing, he does not want to talk about it, and avoids anything that would remind him of it. These symptoms are clearly related to clinical depression, which is a very severe depression, especially the extreme guilt, the sleepless and overt behavior. However, I believe that there is more of a traumatic stress that the solider is feeling. Since traumatic stress is defined as an event that involves actual or threatened death or serious injury to self or others and this then creates intense feelings of fear, helplessness, or horror. A primary example, would absolutely be military combat, and the passage clearly states that ...