With 26 percent of Americans 18 years or older living with a diagnosable mental disorder, it's no wonder mental health is an increasing priority for the average person. But what about the celebrities or famous people we've come to follow so closely? They aren't exempt from mental health issues, either. Some are more private about their mental health, while others strive to raise awareness in hopes of debunking misconceptions about disorders. This slide show includes some of Hollywood and history's most well-known names.

Catherine Zeta Jones may be the new face of bipolar II disorder, but it's no role she hoped to land. Despite now speaking publicly to help remove some of the stigma that comes with the condition, who's to say Jones would've done so it if reports of her treatment hadn't gotten out? "She went to go get some help and some other patient probably in there said, 'Hey, you won't believe who's in here now,'" husband Michael Douglas said during an interview on "The Oprah Winfrey Show." What's the difference between bipolar I and II? According to WebMD, they possess many of the same characteristics -- the highs and lows -- but with bipolar II, the person never reaches full-on mania.

Mel Gibson

Long before he was winning Oscars -- or making headlines for all the wrong reasons -- road warrior Mel Gibson was doing battle with an unseen, off-screen foe: bipolar disorder. Known for his onset pranks and proclivity for after-hours partying, Gibson broached the subject during a 2002 documentary interview with a former classmate. "I had really good highs but some very low lows," Gibson told filmmaker Sally McKenzie for "Acting Class of 1977," which aired on Australian television in 2008. "I found out recently that I'm manic depressive." Numerous articles have been written, linking bipolar mood disorder with artistry. In 2008, a study at the Stanford University School of Medicine found that those with the condition expressed "enhanced creativity," but recommended more research to determine why.

Brooke Shields 

Some celebrities, such as actress and model Brooke Shields  have even written about their experiences. Shields has publicly discussed her bout with postpartum depression after the birth of her daughter in 2003. Lasting longer than your typical "baby blues," postpartum depression includes prolonged feelings of anxiety, worthlessness and restlessness in new mothers. She said that at one point, she "didn't want to live anymore" because her depression was so severe. The actress sought treatment early on and learned to manage her disorder with professional help and medications.

John Nash

Many people hail John Nash as an economic and math genius, especially after he won the Nobel Prize for economic sciences in 1994. But what many people didn't know at the time was that Nash lived with paranoid schizophrenia, a mental health disorder in which people have difficulties telling what's real and what's not, affecting their social responses and ability to think logically at times. During an interview with the Public Broadcasting Service, Nash said his periods of paranoia (during which he heard voices) reflected his wishes to have a more influential role in studies and the world. "People are always selling the idea that people who have mental illness are suffering," he said, proposing that mental health disorders are often misunderstood. Nash said he has made adjustments to live with schizophrenia, which allowed him to continue his life work. His struggle with the mental disorder also inspired the award-winning film "A Beautiful Mind" in 2001.

Carrie Fisher

We're familiar with the Carrie Fisher who donned the Princess Leia buns in the Star Wars trilogy, but offscreen may be a different story. Fisher has struggled with substance abuse and bipolar disorder, she told ABC News in an interview. Bipolar disorder is characterized by severe mood and energy shifts that affect people's ability to do daily activities. Fisher talks publicly about her disorder, telling ABC News Primetime she had "outlasted" her problems. "I am mentally ill. I can say that. I am not ashamed of that," she said.

 Emma Thompson

 Along with 20 million people in the U.S., British actress and screenwriter Emma Thompson has dealt with depression. In an interview with the Daily Telegraph, Thompson said she battled clinical depression in the past, with her career saving her from "going under." Like other people living with clinical depression, Thompson said she felt sad and hopeless, and was unable to get out of bed at times.

Herschel Walker

In recent years, Herschel Walker, a Heisman award-winning running back and former NFL player, has gone public about his troubles with dissociative identity disorder, a complex mental health disorder. People with DID are influenced by two or more distinct personalities, or identities, which prevent them from acting like themselves. Walker has received treatment for the disorder and wrote a book about his experiences. "I feel the greatest achievement of my life will be to tell the world my truth," he said in an interview with ESPN

Michael Phelps

Olympic gold medalist swimmer Michael Phelps has risen to stardom at a fairly young age,and Deborah Phelps, Michael's mother, said she wanted to share Michael's story and his struggles with attention deficit hyperactivity disorder (ADHD). Diagnosed when he was 9 years old, Phelps had trouble concentrating in school, his mother said, but personally prescribed medication and swimming helped Phelps manage the disorder.

Howard Hughes

 known for his wealth, movie production and aviation skills in the early and mid 1900s -- was always in the spotlight for one thing or another. But, ultimately, he is also remembered for his struggle with obsessive compulsive disorder, a condition that causes a combination of unnatural obsessions, anxiety and compulsions, which usually are acted out in repetitive behaviors. Unfortunately, Hughes' OCD led to isolation, increased drug use and his own death, according to the British Broadcasting Company. Notably, his obsession with cleanliness and reputation as a "germaphobe" were evident in his daily life and interactions with his employees. In one repetitive routine, he made his workers use several facial tissues and rounds of hand-washing just to fetch his hearing-aid cord. His career and personal battle with the disorder inspired the 2004 Oscar-winning film "The Aviator." Anxiety is also no stranger to this next celebrity

Paula Deen

is a woman of Southern charm and authentic, real-butter cooking. But Deen had a hard time doing away with her panic attacks and agoraphobia, she said in an interview on the Larry King Live television show. Agoraphobia is when people fear places they know may lead to a panic attack, especially in situations that are difficult to leave. Deen said her attacks began after her father's death, and continued for nearly 20 years. She wouldn't leave the house without a brown paper bag to breathe into in case she had an attack. "I never knew when they were going to hit me, but it's the most terrifying, uncontrollable feeling," she told King. Deen eventually overcame her panic attacks and agoraphobia on her own, but it's common for people with panic attacks to seek professional help.

Music star Elton John discussed his uphill battle with substance abuse and bulimia on Larry King Live in 2002. Bulimia is an eating disorder in which people binge, or uncontrollably consume large amounts of food, and then expel the food by vomiting or using laxatives because they don't want to gain weight. Discussing his substance abuse and bulimia, John said he had been "sober and clean" years. "And it was the best thing I ever did. But, you know, those three words -- I need help. If only I'd said them earlier," John explained.

Craig Ferguson

late-night wit and shenanigans are a must-see for many, and Ferguson occasionally pokes fun at his stint with alcoholism. He's been sober for the past 18 years and has talked publicly about his embarrassing and emotional experiences dealing with his addiction. After submitting himself to a rehabilitation clinic, he found a new perspective in life. "I think what rehab did for me is it began that journey for me, which is a journey to try and get a sense of perspective about myself and where I exist in the world," he told Larry King in 2009. More than 17 million adults in the U.S. have alcohol-related problems. As demonstrated with Ferguson, treatment can be very effective.