Depression is very interesting as the Alter Rebbe whose knowledge of the psyche based on Kabbalah was unparalleled writes, that depression is caused by worries – a person first has to overcome fear (to do this one needs to understand the cause of their fears – one of the great teachings from the Baal Shem Tov (on overcoming basic anxiety which is usually fear of recurrence) is "By finding the good in the bad, the bad will turn to good")