First of all, having days when you feel down, or sad, is normal. We
all have days when we feel blue, or down. It is just part of life. If
those sad, blue feelings become your most predominant feelings
however, like a dark persistent cloud, your emotions may not be just a
"mood" but depression.
full link to the article
http://no4depression.blogspot.com/2008/09/depression-or-just-normal-sadness.html
I hope to leave a comment there as I hope to derive benefit from there
^_^
"Depression requiring clinical treatment can be distinguished from
ordinary sadness by observing how much money the patient has in his
bank account. If the patient has a steady income and sufficient
savings to pay for bi-weekly $200/hr therapy sessions - as well as
prescription coverage - then he most certainly suffers from clinical
depression. If the patient is unemployed and has no prescription
coverage then he suffers from sadness."