Depression is a feeling of severe despondency and dejection, not just over a few days but over a prolonged period of time.
Sometimes you can see a reason for feeling depressed like the end of a relationship, loss of a loved one, moving home and area, losing a job you loved. However, sometimes people think that they have everything in life they could possibly want but still have those feelings of despondency and dejection.
Depression does not discriminate; it can affect anyone. If you think you may be suffering from depression, you can take this test on the NHS website:
Some of the psychological symptoms of depression are feeling tearful, low self-esteem, no motivation, hopeless and having a continually low mood. Physical symptoms can include a change in appetite, lack of energy, insomnia or sleeping more than usual and social symptoms can be not engaging in social activities, seeing family and friends and not wanting to go to work. This list is by no means exhaustive.