Long-time but less deep depression, dysthymia
Studies of the occurrence of depression and dysthymic disorder = dysthymia (a less severe form of the illness) have identified subgroups of people who experience symptoms of depression which do not correspond to the widely accepted stereotype of the depressive illness, but which nevertheless appear significant in terms of the distress and disability they cause to the sufferers.
These show slightly different patterns of symptoms. Often they have long-standing though relatively mild symptoms which nevertheless interfere with their ability to lead life as they wish. They persistently lack enthusiasm, motivation and the ability to enjoy.
There is also an increased risk of suicide.
Short, intensive depressive episodes
Another group experiences intense depressive symptoms but which last only a short time, often just a few days. During this period they show enough symptoms for depression to be diagnosed. Indeed they are at risk of self-harm during this time and often come to medical attention because of an unsuccessful suicide attempt.
However, the depression lifts rapidly without treatment and in retrospect the brief, though dramatic, disturbance of mood does not appear to be connected to adverse life events as one would expect. As yet it is not clear how this group responds to conventional treatments for depression, but it appears to be a large and important group.