Depression - http://www.eyetoeyewales.co.uk/
We all feel happy and sad at different times. Sometimes feeling sad is a normal, appropriate response to what is happening in our lives. Often with time, we find that life changes and the support of those around us help these feeling to go away. However, we feel depressed when sad feelings do not go away, and when they overwhelm a person and stop them from doing the things they normally do. Children and young people are just as likely to get depressed as adults but they just show it in a different ways.
Depression is not always the easiest problem to spot or admit. Some people can talk about feeling unhappy, but others are only able to show how they feel through the way they behave.