Hollywood star Catherine Zeta-Jones has cast a spotlight on a serious mental illness. The Oscar-winning actress recently checked into rehab to treat bipolar disorder, which causes extreme mood swings. One moment they're over-the-top happy, the next moment, depressed and considering suicide. Doctors warn that anyone can develop the dangerous disease at anytime. Why? The main cause is stress. Dr. David Milkowitz is a UCLA psychiatry professor. He says that any extreme life event can trigger bipolar disorder. For example, losing your job or having a baby. Zeta-Jones' publicist says that her illness kicked in after her husband, actor Michael Douglas, was diagnosed with throat cancer. Experts warn that many people don't even realize they're bipolar until something disastrous happens. For example, during a depressed state, they quit their job and spend all of their time sleeping. That's because most of us think nothing of the key symptom - mood swings. After all, it's normal to suddenly feel excited because you scored concert tickets. Or to be upset over a lousy day at work. Experts say that bipolar sufferers experience heightened levels of ups and downs. For example, when they're in a good mood, they're not just happy. They're so excited they go on a thousand dollar shopping spree, even if they can't afford it. The longer the illness goes untreated, the more it can destroy your life, jeopardizing everything from your finances, to your relationships. Right now, bipolar disorder isn't curable. However, you can treat it with medications, like the mood stabilizer lithium, and via psychotherapy - where you talk to a therapist about your stressful issues. If you'd like to go further, check out the National Institute of Mental Health.