Sorrow is the only passion that is not the desire for a certain kind of pleasure. It is the withering of all pleasure.
The way sorrow is described by the Fathers, it contains elements of what we would call depression and grief.
Evagrius states that sorrow is an impediment to the eremitical life while it lasts: there is a danger that the person will not withstand isolation. We add that anyone who suffers from sorrow (or depression or grief) should be cautious about engaging in the Jesus Prayer, also anyone who suffers from bipolar syndrome (manic-depression) or has a family history of it.
It is interesting that the Fathers treat sorrow as a passion like all the other passions. The Fathers treat sorrow as something that we are tempted to engage in, someone that we must fight against.
This is quite different from the orientation of modern psychiatry and psychology, which make the person a passive sufferer. The patristic attitude is that we struggle against these things as against a temptation.
Let us hasten to remark that we do not deny that some or many psychiatric or psychological disorders have a biochemical basis. We are not suggesting that anyone stop their medication or their therapy in order to battle against sorrow in the proper patristic way. That’s silly. Don’t do anything rash or foolish.
However, the Fathers nowhere foresee a spirituality that contains elements of Weltschmerz, that romantic ‘weary of life’ sadness that is sometimes taken for a spiritual state of consciousness. Orthodox spirituality is free of sentimentality, and hence free of Weltschmerz, which is essentially sentimental, although eros for God does enters into the Orthodox spiritual way.