For almost all mental illness, three questions are evaluated, and three treatments are prescribed. This is as true of one time “clinical” depression as Major Depressive Disorder, or as true of Agoraphobia as Bipolar Disorder or even the ‘big one’, Schizophrenia.
Those three things that are evaluated are the duration, the intensity, and the frequency of any mental disturbance. Doctors and therapists don’t tend to come right out of the gate with these questions. They generally attempt to draw them out by asking about your history, how much your everyday life as been affected, things like that.