A 22 year old man is brought to the doctor by his roommate. The roommate has known the patient for years, but says about a year ago, the patient started acting weirder without any trigger. The patient would have episodes of not leaving his room, not talking, not responding, and not wanting to do anything. There have been 1-2 past episodes. About a week ago, the patient started acting in the same way. Indeed, the patient has a blank look on his face, responds to few verbal commands, but withdraws to noxious stimuli. The patient has no interest in his environment. He gives monotonous one-word responses to some questions. He displays no emotional range, and when asked, says he feels "bad." The roommate says the patient dropped out of community college a few months ago, has never held a job for longer than a month, and has almost no friends. Mental status exam shows poor attention, language, memory, and executive function. When you raise his left arm over his head and let go, he keeps it there even though the position is awkward. Yet when you move him in other ways, he seems to have purposeless resistance.
Challenge: What's the most likely diagnosis here?