Catherine Zeta

The revelation that the seemingly unshakable actress Catherine Zeta Jones has been diagnosed with bipolar disorder illustrates the hallmarks of the disease: it can strike at any time in a person's life and is often brought on by prolonged stressed.

Zeta-Jones, 41, fell victim to the disorder's wild mood swings after her husband Michael Douglas went through a high-profile battle with stage IV throat cancer and then endured a court fight with Douglas' first wife over proceeds from the "Wall Street" movie sequel.

Bipolar disorder, also known as manic depressive illness, is a mental illness characterized by mood swings between the two psychological pulls of depression and euphoria.

"It can start at any time in a person's life and it's a lifelong illness," Dr. Igor Galynker, director of the Family Center for Bipolar Disorder at Beth Israel Medical Center told ABC News OnCall.

Zeta-Jones is said to have been diagnosed with bipolar II, which is a form of the disorder which is characterized by longer low periods.

Stress is one common trigger for bipolar disorder, according to the National Institutes of Mental Health. The condition can also be spotted if someone has a prolonged feeling of agitation, trouble sleeping, major changes in appetite, and thoughts of suicide.

Zeta-Jones has had plenty of stress over the past year. Last year, Douglas, 66, the father of Zeta-Jones' two children, was diagnosed with stage IV throat cancer. While Douglas announced in January that he was cancer free, he and Zeta-Jones have more recently had to battle Douglas' first wife, Diandra, who is suing Douglas for a portion of the royalties from his movie, "Wall Street: Money Never Sleeps."

"After dealing with the stress of the past year, Catherine made the decision to check into a mental health facility for a brief stay to treat her bipolar II disorder," Zeta-Jones publicist said in a statement.

There's hope for most who have been diagnosed with bipolar disorde, according to Galynker.

"It is not curable, but it is treatable with medications and psychotherapy." said Galynker. "People with bipolar illness can have productive lives like anybody else, once they're in treatment and compliant with treatment."