Unmotivated Sadness
St. John Cassian tells us that ‘it sometimes happens that we are suddenly filled with an anxiety that has no cause; we feel overwhelmed by a sadness for which no motive can be found.’ He also says that there are two different kinds of sadness: the first consists of all those varieties considered above, ‘the second comes from unreasonable mental anguish or despair.’

Mental Disorders & Spiritual Healing: Teachings from the Early Christian East
Jean-Claude Larchet