A 43-year-old man is admitted to the neurology service after he went blind suddenly on the morning of admission. The patient does not seem overly concerned with his sudden lack of vision. The only time he gets upset during the interview is when he is discussing his mother＇s recent death in the countryside he was supposed to bring his mother to the city, but did not because he had been using drugs and did not save the necessary money. Physical examination is completely negative. Which of the following is the most likely diagnosis