A Sudden Shift in Moods

But the milder condition can still be disabling and disorienting. "People who have more or less continuous mood fluctuations, as people with cyclothymia do, can end up with more limitations in life than people with major disorders," Goodwin said. "Because they don't know how they're going to feel from day to day, they don't have a firm footing in relationships or in their work. And they lack the ability to have confidence in what a mood means, whether it's a signal about a relationship or a work situation or a spontaneous change."

The German psychiatrist Ewald Hecker introduced the concept of cyclothymia in 1877, but its definition has evolved from a mild problem with mood to its current status, in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), as a mood disorder alongside bipolar disorder and major depression. Cyclothymic disorder also appears in the International Classification of Diseases (ICD-10), published by the World Health Organization.

Yet the condition has traditionally been overlooked by those who have it and the doctors who've treated them. This may be because there's a fine line between pathological and normal mood fluctuations.

"The threshold is when a person is really having trouble in their relationships or at work or in school," said Kleinman. "Often, he added, "it's a friend or family member who says, 'I think there's a problem here.' "

Complicating matters, people usually seek professional help when they're feeling down, not up. " . . . They come in because they're depressed or hurting," Goodwin said. "They don't come in saying, 'Doctor, I'm hypersexual or too creative.' We'd all love to have that." People who come in during a down period of cyclothymia may be misdiagnosed with -- and mistreated for -- unipolar depression.

In therapy, there's also a mood-driven memory bias: When people are depressed, they tend to remember their past depressions, not their periods of euphoria or super-productivity, according to Goodwin. So what they report can give a mental health professional a skewed picture of what's really been going on with them.

Cycles of Vulnerability

The cause of cyclothymic disorder, which usually begins in the teens or twenties, is unknown, but there appears to be a genetic component. People who have a family history of bipolar disorder are particularly susceptible. In a recent study involving healthy, symptom-free volunteers, researchers in France found that a cyclothymic temperament clusters in families with affective disorders, particularly in those with a legacy of bipolar disorders or depressive disorders.

There's also likely an environmental influence, since stress, personal loss, drug or alcohol use, or even insufficient sleep can trigger episodes or mood fluctuations. In people with cyclothymia, "the brain has less capacity to buffer itself against what's happening in the environment," Goodwin explains.

Linda Sexton was diagnosed with cyclothymia in 1983, when her children were toddlers. A daughter of the poet Anne Sexton, who suffered from severe depression and committed suicide when Linda was 21, Linda began to have mood swings when she struggled with disciplining her children.

"When I found myself replicating the spanking I had experienced as a child and promised I wouldn't do, I went into therapy," said Sexton, who lives in the San Francisco Bay area. "I was having periods of depression during which I was unable to complete tasks and didn't feel like I had anything to offer my children, which was killing me because I considered them the most precious thing in my life." Then she'd have surges of hypomanic behavior -- for instance, going out and buying 10 pairs of shoes at a time.

Gradually, her cyclothymia got worse, especially when she was treated with antidepressants. She had free-floating anxiety and surges of self-hatred. Her marriage fell apart. In 1996, Sexton was diagnosed with a full-blown bipolar disorder.

At this point, diagnosing cyclothymia isn't an exact science.