Depression, a mental illness that is often characterized by prolonged periods of sadness and melancholy, experts from the field of psychiatry say.
But just because one person is moping around and just generally hating the world around him or her, doesn't mean that it's already depression, but if this kind of behavior, the feeling of emptiness, loss of self-worth and absolutely no hope for happiness just goes on and on, then, yes, that individual is very much, indeed, depressed.
Still, there are various types of depression, from Manic or Bipolar depression - characterized by sudden and extreme changes in one's mood wherein one minute he or she is in an elevated state of euphoria while the next minute (day or week) he or she is feeling to be in a personal hell, Postpartum depression - characterized by a prolonged sadness and a feeling of emptiness by a new mother wherein physical stress during child birth, an uncertain sense of responsibility towards the new born baby can be just some of the possible factors why some new mother go through this, Dysthimia - characterized by a slight similarity with depression, although this time, it's been proven to be a lot less severe, but of course with any case, should be treated immediately, Cyclothemia -