Is anxiety & depression the same thing?
Many persons who mostly have symptoms of depression also have anxiety, and many persons who mostly have symptoms of anxiety also have some depression. One way to look at this is that different parts of the brain may be more involved with anxiety and others depression, and there are actually studies showing some of these differences. So, if the main problem is an illness of depression, then anxiety can be thought of as a symptom, something akin to the symptoms of cough and fever when someone has an illness of a cold. In this light, depression could also be thought of as a symptom of an illness of anxiety when anxiety seems to be the major problem. There may also be situations where both brain areas are having trouble, and/or that anxiety and depressed mood are really just different expressions of similar pathology.
Another confusing issue is that while some psychiatrists prefer to classify both anxiety and depression as “mood disorders”, others (and the current official diagnostic systems) consider them separate classifications. Because anxiety and depression commonly coexist, Counseling Tokyo thinks it probably makes sense to consider both anxiety and depression along the spectrum of a mood disorder (see this reference).
The silver lining thru all this confusion is that both the psychotherapy and pharmacotherapy of these problems largely overlaps so that it is not so crucial what the exact classification is. Perhaps a more important point to make for persons with anxiety and/or depression is that they do not have 2 illnesses of anxiety AND depression; they have one illness that causes both feeling states, and knowing this is often a relief in itself.