Warning signs of serious depression                    

         Social withdrawal

         Poor communication and sharing

         Reduced effort and involvement with others

         Changes in friends, preferring to be around people who are angry or negative

         Loss of interest in things you used to like doing

         Insomnia or increased or decreased sleep

         Defiance

         Dishonesty

         A strong "I don't care" attitude

         Preoccupation in dress, color, poetry, music, peers or attitude

         Poor impulse control

         Reduced honest cooperation with authority figures

         Discussions of lack of pleasure in life or reason to live

Source:  http://www.teen-matters.com/depression.html.