An 18-year-old boy attending high school and living with his mother presents with low energy and feelings of profound sadness. He explains that these symptoms started about 10 weeks ago, seemingly out of nowhere. Prior to symptom onset, the patient felt "on top of the world" for approximately 5 days. However, he reports having experienced a period of sadness once before. He has not been able to sleep for the past few weeks and cannot concentrate or sit still. He reports not being interested in food and has lost about 8 lb in the past 2 months (height is 5 ft 9 in; weight is 149 lb; body mass index is 22). He reports vaping and drinking socially. The patient has no significant medical history, but family history is significant for maternal uncle with schizophrenia. Physical examination is unremarkable. The patient scores 14 on the Patient Health Questionnaire–9, and his mother reports a significant departure from his usual personality.