Cricketer Andrew Flintoff speaks out about depression
11 January 2012 Last updated at 13:31 GMT
Professional athletes often experience extreme highs and lows, and can often be the last to realise they have depression.
Cricketer Andrew Flintoff, who has suffered from the condition, has been exploring the issue for a BBC documentary.
The Hidden Side of Sport is on BBC One at 2245 on Wednesday 11 January, and available later on the iPlayer.