A 41-year-old male presents to a psychiatric clinic reporting that he has felt "low" for as long as he can remember. He describes chronic low mood, poor self-esteem, fatigue, and difficulty making decisions that have been present most days for at least the past 5 years. He has never experienced a period of 2 or more months without these symptoms. Over the past 6 weeks, his symptoms have markedly worsened: he now reports anhedonia, a 15-pound weight loss, insomnia with early morning awakening, psychomotor retardation, and passive suicidal ideation. He states, "I've always been a sad person, but this is different — I can barely get out of bed." His PHQ-9 score is 22. What is the MOST accurate diagnostic formulation?