Unhappiness or unhappiness (low mood) is only one of the symptoms of depression, in addition to diminished interest or loss of pleasure, lack of energy, poor concentration, low self-esteem, self-guilt or feelings of worthlessness, perception of a bleak and pessimistic future, self-injurious or suicidal behavior, sleep disturbances, and decreased appetite. If several of these are satisfied and persist for more than 2 weeks and have a definite impact on work, study and life, it is possible that you have depression.