Final answer:
Lilly is likely suffering from Dysthymic Disorder, a chronic form of depression with persistent low mood, which differs from Major Depression in duration and severity of symptoms.
Step-by-step explanation:
Lilly, who is 35 years old and has been feeling "down in the dumps" most of her life, has started therapy and is most likely suffering from Dysthymic Disorder (C). Dysthymic Disorder, also known as Persistent Depressive Disorder, is a form of depression characterized by a chronic, long-term state of low mood and apathy. Unlike Major Depression, which involves severe symptoms that can significantly interfere with daily activities and may include episodes of intense sadness, loss of interest in activities, and other debilitating symptoms that are present for at least two weeks, Dysthymic Disorder consists of a persistently low mood that lasts for years but may not reach the intensity of major depressive episodes.
While focusing on mood disorders, it’s important to note that other mental health disorders such as Bipolar Disorder, Generalized Anxiety Disorder, and Antisocial Personality Disorder have distinct symptoms and patterns that differentiate them from Dysthymic Disorder.