This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Neurotic, Stress Related and Somatoform Disorders, Subject name: Psychiatry
Two months after knowing that his son was suffering from leukemia, a 45 year old father presents with sleep deprivation, lethargy, headache, and low mood. He interacts reasonably well with others, but has absented himself from work. The most probable diagnosis is: 
Select and explain. 
A. Depression, B. Psychogenic headache, C. Adjustment disorder, D. Somatization disorder
C: Adjustment disorder
Answer: C: Adjustment disorder 
Explanation: Here, the diagnosis is adjustment disorder. The symptoms are not severe enough to qualify for the diagnosis of depression and there is a clear history of a stressor (diagnosis of leukemia in son). The symptoms of adjustment disorder usually sta within 3 months of the stressor