This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Mood disorders, Subject name: Psychiatry
Which of the following is most characteristic of sleep in a 45-year-old woman with major depressive disorder? 
Select and explain. 
A. Sleeping too many hours at night, B. Falling asleep suddenly during the daytime, C. Walking up too early in the morning, D. Having difficulty coming fully awake after sleep
C: Walking up too early in the morning
Answer: C: Walking up too early in the morning 
Explanation: Although excessive sleeping may also occur, the sleep problem most characteristic of the major depressive disorder is early morning awakening, commonly called "terminal insomnia." Falling asleep suddenly during the daytime is narcolepsy, and cessation of breathing during sleep is sleep apnea. "Sleep drunkenness" involves difficulty in coming fully awake after sleep.