Catherine Zeta Jones has received treatment for bipolar disorder after dealing with the stress of her husband's battle with throat cancer.
Zeta Jones, 41, made a decision to check into a "mental health facility" for a brief stay, said her publicist.
Michael Douglas, who was diagnosed last year, said in January his tumour had gone and he was beating the disease.
Last September, Zeta Jones said she was "furious" that doctors failed to detect the cancer earlier.
Bipolar disorder, also known as manic depression, causes severe mood swings, that usually last several weeks or months.
Zeta Jones's publicist Cece Yorke said the actress sought treatment for the condition following the stress of her husband's cancer fight.
"After dealing with the stress of the past year, Catherine made the decision to check in to a mental health facility for a brief stay to treat her Bipolar II disorder," said Yorke.
"She's feeling great and looking forward to starting work this week on her two upcoming films."
It is unclear when Zeta Jones, who is from Swansea, was diagnosed with bipolar disorder or where she received treatment.
Mark Davies, from mental health charity Rethink, said the actress had shown courage in revealing the disorder as there was still a stigma around mental illness.
"Although she'll be feeling pretty fragile and vulnerable, she will have - in a sense - given some comfort to a lot of other people who are probably suffering in silence and probably feeling a great deal of fear," he added.
Mr Davies said the disorder could be triggered by a range of factors and that no individual case was the same.
He said the star was likely to be given medication and talking therapy, recognised as increasingly effective in cases of serious mental illness.
About 1% of the population suffers from bipolar disorder.
Alun Thomas of the Welsh mental health charity Hafal said: "The important part of this news is Catherine has sought help.
"Many parts of the press can sensationalise this but I think it's important to discuss the issues sensitively and raise awareness.
"Many creative and famous people have been diagnosed with bipolar disorder... there are many people out there who have recovered and gone to be very productive in their lives."
Shortly after her husband was diagnosed with cancer, the actress revealed she was "furious" that doctors failed to detect the disease earlier.
In an interview with People magazine last September, she said: "He sought every option and nothing was found. I knew something was up. He knew something was up."
"It makes me furious they didn't detect it earlier," she added.
The star, who won a best supporting actress Oscar for her role in Chicago, was made a CBE by the Prince of Wales at Buckingham Palace in February.
She first found fame in the UK on the small screen in the 1991 comedy drama, the Darling Buds of May, before heading to Hollywood to star in Entrapment, Traffic and The Mask of Zorro.