How do I know if I have depression or am just sad?

Sadness is a passing response to events. Depression persists most of the day, nearly every day, for two weeks or more, and includes loss of interest or pleasure, plus changes in sleep, appetite, energy, concentration, or self-worth. When it impairs daily functioning, seek assessment.

Two questions used for screening: over the past two weeks, how often have you had little interest or pleasure in doing things, and how often have you felt down, hopeless or depressed?

Physical causes should be excluded too — hypothyroidism, anaemia, vitamin B12 or D deficiency and sleep apnoea can all present as low mood and low energy.