Is depression something that can go away without treatment, either medical or therapy, or do you have to get treatment in order to get over it?
It is true that episodes of depression can go away without treatment--it is also true that untreated depression can become chronic and develop a wide range of complications.
An episode of depression that is not treated may last 6 months or more, even many years. There are risks of not treating depression--it has been shown that as many as 5 to 15% of people with untreated major depression commit suicide.
Also, there are a wide range of possible bad outcomes of untreated depression, ranging from increased absenteeism at work to increased alcohol use, smoking, and poorer physical health. Brain imaging studies have shown that untreated (or chronic) depression is associated with shrinkage, or atrophy, of parts of the brain related to working memory and higher cognitive functioning.
When treated, the symptoms of depression generally resolve over 1 to 2 months. Finally, a number of medical conditions can present as "depression"--so a good medical evaluation is indicated when a person becomes depressed. .
So, in summary, symptoms of depression that last for a month or more should be evaluated, and generally require treatment--medication, psychotherapy, or both.