Eric Millegan, of Fox's hit show "Bones," woke up early one Los Angeles morning in 2005 and everything felt dark, heavy and awful. Then, almost as quickly as the helpless feelings began, he popped out of the depression and decided to pay an impulsive visit to Disneyland, a quintessential "happy place." Upon arriving, Millegan, then 30, bought a piece of pizza, sat down and started crying uncontrollably. For no reason.

"I knew then, I was like, 'Something's wrong with me. Why am I crying? What's going on here?'"

That intense switching-of-gears was a symptom of the illness he didn't know he had: bipolar disorder. As Mental Illness Awareness Week unfolds, Millegan's story is one of many that illuminates what it's like to live with a mental disorder, like bipolar, and underscores the importance of seeking help.

Diagnosing Bipolar Disorder

An estimated 2.6 percent of U.S. adults have bipolar disorder, characterized by changes in mood, energy and activity levels that can disrupt daily life, according to the Depression and Bipolar Support Alliance, or DBSA. On average, people tend to develop the disorder around age 25, though for some, like Millegan, it doesn't obviously surface until much later.

There are four basic types of bipolar disorder, according to the National Institute of Mental Health: bipolar I (the classic form that Millegan has), bipolar II (a milder form), cyclothymic disorder and "other specified and unspecific bipolar and related disorders."

About 1 percent of the U.S. population has bipolar I, followed by another 1 to 2 percent with bipolar II; as many as 2 to 3 percent of sufferers have spectrum conditions, according to Dr. Michael Thase, a psychiatry professor at the Perelman School of Medicine at the University of Pennsylvania.

Alarmed by his episode, Millegan, now 42, sought help from a psychiatrist.

That therapy session was what Millegan now refers to as "a bipolar show." He discussed his depression, then proceeded to jump around the room happily.

"Right then and there, she was like, 'Well, you're bipolar.'" Millegan wondered if the doctor had accurately diagnosed him; what if he had left out critical details of his story or experience? But he was missing the point.

"'It wasn't what you told me. It was the way you told me,'" Millegan recalls his psychiatrist saying.

Treating Bipolar Disorder

In some ways, Millegan was lucky. "All too often, people who have bipolar disorder either don't know they have it [or] aren't receiving treatment [and] they use alcohol and other substances as a sort of self-medication," says Allen Doederlein, president of the DBSA.

Treating bipolar disorder – a critical part of managing the illness – is a delicate dance involving four key components, Doederlein says: medication (the basic kinds are mood stabilizers and antipsychotics, according to Thase); talk therapy (like cognitive behavioral therapy, designed to help break negative thought and behavioral patterns); peer support; and lifestyle interventions (prioritizing sleep, healthy eating and exercise).

Millegan started taking medication, though it took a couple of years for him to have consistently good days; to be "balanced." And he was, for some time.

But following a change in medication three years ago to alleviate a known side effect of certain drugs – weight gain – Millegan went to England to sign autographs at a convention, which led to another breakdown and suicidal feelings. Millegan was bombarded by something that, to the average person, wouldn't seem like a problem: being told you're amazing and how much you're loved. But when you have bipolar disorder, your high can get too high. The disease magnifies feelings: Something small could trigger suicidal thoughts, while a "high" can spiral out of control. About 20 percent of people with bipolar disorder die by suicide, according to the DBSA.

In England, he became infatuated with a straight man he just met and barely knew – "a nice guy" – even though Millegan himself was married. These heightened emotions again threw Millegan off-balance, and he ultimately was placed on a higher dose of a prior medication to manage his disorder.

Millegan's experience highlights the importance of receiving the correct diagnosis, medication and treatment – and being cognizant of possible flare-ups when part of the treatment plan changes or no longer works. "People are more likely to get symptomatic during medication switches than during times that medications are stable," Thase says.

For people with bipolar disorder, life's milestones can cause emotions to run effervescent then immediately flat like an old soft drink. The death of a loved one, divorce, marriage or having a child all greatly impact someone's life, but for most bipolar individuals, it's the chronic heightened manifestation of these emotions that causes problems. Even a small disappointment – like Millegan's experience with a man he had just met – meant a total balance shift.

Helping Others Get Help

Millegan first spoke publicly about his mental illness with the Huffington Post in 2010. His goal was to help others going through it.

The stigma surrounding mental illness – something Millegan says he hasn't directly experienced – can prompt insensitive questions from friends and loved ones. Why can't you just get over it? Are you ever going to be normal?

The short answer: It's complicated. "People can influence their chances of being well or ill based on the decisions and things they do in living their life," Thase says. "But at the end of the day, there are some aspects of our body, and especially our brain, that are kind of out of our willful control. And if you're stuck with this illness, just by the luck of the draw, and you start to go into a manic episode, no amount of willpower may protect you from that."

But early recognition and prompt, consistent treatment is vital to helping those living with bipolar disorder cope and thrive, Thase says. If financial or insurance barriers exist, he adds that most communities offer basic-care services, and notes that most medications for bipolar disorder are available generically. Medicaid is the biggest mental health services payer in the U.S., according to its website.

Before Millegan's diagnosis, he didn't have the same compassion he has now for those with any mental illness.

What's important to remember about bipolar disorder – and arguably all mental illness, of which 1 in 4 Americans ages 18 and up experiences in a given year – is that it's an exaggerated reflection of what it means to be human. As Thase says, "The illness is intertwined with humanness."