Catherine Zeta-Jones: What Is Bipolar II Disorder?

Warner Bros.

The actress was treated for the mental illness before shooting her new film.

Catherine Zeta-Jones briefly checked into a facility to treat her bipolar II disorder.

The actress is "about to start working, and wanted to make sure she's in top form, which she is," reported, referring to her movie Playing the Field, co-starring Gerard Butler.

Just what is Bipolar II Disorder?

According to WebMD, it's "similar to bipolar I disorder, with moods cycling between high and low over time. However, in bipolar II disorder, the 'up' moods never reach full-on mania. The less-intense elevated moods in bipolar II disorder are called hypomanic episodes, or hypomania."

The site also notes that "most people with bipolar II disorder also suffer from episodes of depression. This is where the term 'manic depression' comes from. In between episodes of hypomania and depression, many people with bipolar II disorder live normal lives."

Zeta-Jones -- who is just one of the Hollywood heavyweights who suffers from the mental illness -- has had a roller coaster year. Her husband, Michael Douglas, revealed earlier this year that he was cancer free.

"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," says her rep. "She’s feeling great and looking forward to starting work this week on her two upcoming films."

Twitter: @LKPE