The Girls Aloud singer is struggling to deal with the break-up of her relationship with fiance Tom Crane in September and has decided to book herself into an unknown rehabilitation facility abroad after hitting "rock bottom".
A source told The Sun newspaper: "She`s been through a traumatic time in her personal life and had to honour her work commitments on top. She needs some time out to clear her head.
"Splitting from Tom has played a huge part in her decision to seek help. She has hit rock bottom."
Sarah, 31, was due to marry next summer, but the couple decided to separate after a number of arguments.
Since then, friends have urged the blonde beauty - who has been dating Tom for four years - to deal with her issues by seeking help, but she continued to "bury her head in the sand".
The source added: "It all just got the better of her. She had been with Tom for a long time. All her plans for the future suddenly came crashing down.
"Some of her closest friends had suggested she seek help over the last few months, but she refused.
"She was burying her head in the sand, but now she is getting support."
A representative confirmed: "SarahHarding has entered a treatment centre for depression and alcohol addiction."