Today, Zeta-Jones' publicist revealed that the actress recently sought treatment for bipolar disorder.
"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," her publicist said in a statement. "She's feeling great and looking forward to starting work this week this week on her two upcoming films."
Bipolar disorder is also called manic-depressive illness. The disorder is most known for the unusual shifts in mood and energy that those with it experience. Sufferers can go through what is known as a manic episode -- an overly excited or joyful state -- or a depressive episode -- a state of unusual sadness or hopelessness.
Bipolar II disorder is not as severe as bipolar I. According to the National Institute of Mental Health, while those with bipolar I typically experience mania and intense mood episodes that can last at least seven days and may require hospitalization, bipolar II usually results in less intense depressive episodes.
While bipolar disorder often develops in a person's late teens or early adult years, it has been known to develop later on in life as well.
Zeta-Jones, 41, was outspoken about her anger after Douglas, 66, was diagnosed with throat cancer in August 2010.
"It makes me furious they didn't detect it earlier," Zeta-Jones told People magazine. "He sought every option and nothing was found."
Douglas' cancer wasn't the only stress in the couple's life. Last year, Douglas' ex-wife took him to court seeking a some of his profits from his "Wall Street" sequel, which was released in 2010 but was based on the iconic film that he made while they were married, which she said entitled her to a share.
Zeta-Jones reportedly turned down roles to be by Douglas' side through his legal and physical battles. In January, Douglas noted that his cancer fight drew him and Zeta-Jones closer.
"One thing that all cancer survivors talk about is a new depth of feeling that you have for loved ones," he said while receiving an award at the Palm Springs Film Festival. Zeta-Jones was at the festival with him.
"It's made us even closer," he added, "and certainly there's a depth of emotion and an appreciation of your daily life that you didn't have before."
Zeta-Jones and Douglas married in 2000. They have two children together, Dylan Michael Douglas and Carys Zeta Douglas.
ABC News' Dan Childs contributed reporting.