Jessica is a 28 year-old married female. She has a very demanding, high stress job as a second year medical resident in a large hospital. Jessica has always been a high achiever. She graduated with top honors in both college and medical school. She has very high standards for herself and can be very self-critical when she fails to meet them. Lately, she has struggled with significant feelings of worthlessness and shame due to her inability to perform as well as she always has in the past. For the past few weeks, Jessica has felt unusually fatigued and found it increasingly difficult to concentrate at work. Her coworkers have noticed that she is often irritable and withdrawn, which is quite different from her typically upbeat and friendly disposition. She has called in sick on several occasions, which is completely unlike her. On those days, she stays in bed all day, watching TV or sleeping. At home, Jessica’s husband has noticed changes as well. She has shown little interest in sex and has had difficulties falling asleep at night. Her insomnia has been keeping him awake as she tosses and turns for an hour or two after they go to bed. He has overheard her having frequent tearful phone conversations with her closest friend, which have him worried. When he tries to get her to open up about what is bothering her, she pushes him away with an abrupt “everything’s fine”. Although she has not ever considered sui-slide, Jessica has found herself increasingly dissatisfied with her life. She has been having frequent thoughts of wishing she were dead. She gets frustrated with herself because she feels like she has every reason to be happy, yet can’t seem to shake the sense of doom and gloom that has been clouding each day as of late. What is Jessica's diagnosis? Explain your answer.