Some people have had lifelong phases of feeling flat and low, not being able to enjoy things or function as they would like to. They may feel that they have never been able to find a way to cope with these depressed phases. For others, these kinds of feelings are a new experience and feel completely alien - it seems hard sometimes to work out what is causing them.
Some typical features of depression are: lack of interest or pleasure in doing things that you normally find enjoyable; feeling very self-critical; feeling hopeless and pessimistic about your future; having thoughts that you would be 'better off dead'; loss of energy and tiredness; sleep problems (either getting to sleep or waking early); loss of appetite or over-eating; loss of sexual interest.