Particularly when used in a narrative piece, I often notice liberal use of the word "depression", which often seems to be used as a synonym for "sad." Can one be depressed for a few moments in time? Or is depression a long-term state of mind?
I have heard plenty of grousing from a) mental health professionals, b) sufferers from clinical depression and c) the nearest and dearest of the latter, about the "cheapening" of this word to mean, as you say, "sad". Having the blues, the megrims, being melancholy, down in the mouth or whatever is part of the human condition: clinical depression is a neurochemical disorder. If we stay with this usage, the answer to your first question has to be "no" -- being depressed for five minutes would be like having a transitory attack of lung cancer.
One might go further and say that our culture "medicalises" sadness where others do not. A well-educated Japanese gentleman wets his sleeves at the falling of the leaves, and a Nihonophone brother of a friend gave me this marvellous bon mot: "We see more clearly through tears". He says that the American pharmaceutical companies are busy redefining the culturally accepted or admired melancholy of Japan as a problem requiring the purchase of their products. Well, they would, wouldn't they?
From whence comes our notion that we have to be happy all the time? Perhaps the Reformation, after which being miserable raises doubts as to whether you are truly Saved.
It is often a long time from wiktionary :
In psychotherapy and psychiatry, a state of mind producing serious, long-term lowering of enjoyment of life or inability to visualize a happy future.
I used to suffer from depression, but now I'm mostly content with my life.
In psychotherapy and psychiatry, a period of unhappiness or low morale which lasts longer than several weeks and may include ideation of self-inflicted injury or suicide.
In french, it is a mind weakness state, not specified in time. It is often linked to the major depressive disorder.
The word 'depression' refers to a condition. It begins as an emotion of 'sadness and anger' leading to 'frustration' and then becomes a condition ' depression' Read here for more. information on depression