A 30-year-old man comes to his primary care physician to discuss his “negative mood” for two months. The patient’s partner tells the physician he is not attending activities he previously enjoyed, like playing golf or hanging out with his friends. They state, “He seems emotionally detached from everyone.” She adds that he has been increasingly irritable with spontaneous outbursts of anger several times over the past two months. The patient is a police officer and confides that his symptoms appeared after he witnessed the death of his partner three months ago. The patient states, “Every night, I keep seeing my partner getting shot, and I can’t sleep.” He has a past medical history of depression
in his youth, treated with sertraline
. Which of the following is the most likely diagnosis?