Many Americans have bipolar disorder. Understand the cause, treatment of this condition.

When it comes to mental health disorders, few are as prevalent - or as misunderstood - as bipolar disorder. It's a mental health condition that some 4.4% of U.S. adults experience at some time in their lives, according to The National Institute of Mental Health (NIMH). That's about 11.3 million people who have experienced the disorder in their past or are currently living with it.

While the degree to which bipolar disorder affects one's life varies from person to person, it can have a major impact on one's lifestyle, livelihood, relationships and day-to-day activities.

What is bipolar disorder?

Bipolar disorder, formerly called manic depression, is defined by the NIMH as a mental illness that causes unusual shifts in a person’s mood, energy, activity levels and concentration. "It's high highs and low lows can impede one's ability to function daily," says Rwenshaun Miller, LCMHCS, a mental health professional practicing in North Carolina.

There are three types of bipolar disorder, each ranging in level of severity:

• Bipolar I disorder is the most severe and is defined by manic episodes that last at least 7 days. Manic episodes are extreme increases in energy or euphoria on one side, or feeling depressed or unusually irritable on the other. During these lengthy episodes that are common in this first type of the disorder, the person's highs or lows will usually cause them to behave severely enough that they will require immediate medical care.

• Bipolar II disorder is similar to the first type, but its manic episodes are less severe. These toned-down shifts in mood and feelings are called hypomanic episodes.

• Cyclothymic disorder is defined by episodes that are even less intense than those of the second type - and not lasting long enough to qualify as hypomanic or depressive episodes.

"Since there are no specific tests for bipolar disorder, diagnosis is based on symptoms and a medical work-up to rule out other possible medical causes for the observed symptoms," says Robert Beech, MD, PhD, a psychiatrist at Yale School of Medicine.

What causes bipolar disorder?

Like most psychiatric illnesses, Beech says the exact cause of bipolar disorder remains unknown, "but appears to include both genetic and environmental factors." On the genetic side, there may be chemical imbalances in the brain; and he explains that if one parent has bipolar disorder, the risk of their child developing the condition "is about 10%." If both parents have bipolar disorder, the risk increases to about 40%. In either case, the odds are "lower than what would be expected for a single gene causing it, even if the mutation were recessive," he says.

Of potential environmental causes, trauma experienced in one's childhood is common. A history of "engaging in illicit substance use, experiencing particularly stressful situations or chronic stressors and climate or changes in the seasons have all been linked to causes of manic or depressive episodes," explains Chase Anderson, MD, an assistant professor of clinical psychiatry at the University of California, San Francisco.

What does bipolar disorder feel like?

Also similar to other mental health disorders, each person may experience symptoms related to bipolar disorder differently. "There is a spectrum," says Anderson. He explains that an acronym that is helpful when thinking about how bipolar disorder symptoms feel or manifest is DIGFAST: D for distractibility, I for irritability or irresponsibility ("such as making decisions and choices outside of what is normal for the person," he says), G for grandiosity, F for flight of ideas (jumping from one unrelated thought to another), A for increase in activities, S for sleep changes, and T for talkativeness - "this can be known as pressured speech where the person is hard to interrupt because they are talking so quickly," Anderson says.

Miller lives with bipolar disorder himself and says it causes people to experience "a high sense of self, like they are superhuman." He explains that it also makes one feel a decreased need for sleep and/or feel an excessive appetite for pleasurable activities. People with bipolar disorder also frequently experience "racing thoughts," he says. On the opposite end, the person might experience depressive episodes that cause them to "have a low sense of self, sleep too much, have trouble concentrating or making decisions, feel hopeless or experience a general lack of interest in almost all activities."

The experts say that if you or a loved one is experiencing symptoms you think may be related to bipolar disorder, it would be wise to consult with a mental health professional. Because the disorder affects tens of millions of people worldwide, there are a lot of therapies, mood-stabilizing medications and strategies that are known to be helpful.

Some such strategies "include keeping a log of your sleep, meditation, monitoring for when your stress levels rise and avoiding substance use," says Anderson. He says getting the right medication or talking with a therapist can be especially helpful, "not only because this can provide space to talk about what it is like for a person to live with bipolar disorder and how they want to navigate their life, but also to have a professional in mental health who can monitor for signs or symptoms of re-emerging mania."

We care about depression and anxiety. Where's the empathy when it comes to manic episodes?

This article originally appeared on USA TODAY: What is bipolar disorder?