Range of depression
Depression has a range of meaning-from a description of normal unhappiness, through persistent and pervasive ways of thinking and feeling, to psychosis. It is clear that it is a very common event as it is also clear that it is difficult to differentiate between depression as an illness and when it is an understandable psychological reaction to the ups and downs of life.
What is depression?
The criteria that have been most frequently used to define the type of depression that is considered an illness are the severity of it and the length of time it lasts. Sometimes though a mood state may be considered abnormal not because it is qualitatively different or persisting for a lengthier period than expected, but because they seem out of context, in the sense of not being plausibly the result of events or circumstances.