Until her 40s, Carol Brown's life was plagued by frequent panic attacks -- an experience familiar to some 2.4 million Americans.
The first such attack occurred when she was 16 years old and riding in an elevator. Suddenly, said Brown, "my heart started racing, my hands were sweating, my breathing was shallow. I thought I was going to die. I didn't tell anybody. I thought I was losing my mind."
In a panic attack, a person feels a rush of fear or distress with no sense of its cause. This is often accompanied by heart palpitations, shortness of breath, numbness or tingling, lightheadedness, flushes, chills, nausea, sweating, trembling or shaking.
Many people rush to the hospital emergency room, fearful they are having a heart attack.
The first attack often makes people so afraid of another that they avoid anything associated with it. Women have more panic attacks than men.
For Brown, 54, of Belmont, Mass., that meant avoiding elevators. Later, after suffering panic attacks on the highway and in a supermarket, she avoided those places.
Years ago, doctors would likely have attributed panic attacks like Brown's to some deep psychological problem. While that diagnosis still persists, they are now more likely to suspect biology.
"The biological hypotheses for panic disorders are based on several observations," said Dr. Srini Pillay, director of the panic disorders research program at McLean Hospital in Belmont.
"Pharmacologic medications can stop panic attacks and panic attacks can be induced by various compounds," he said. Panic attacks also occur "out of the blue, suggesting some sudden alteration in chemistry."
They can also occur when a person is not anxious, and even occur during sleep, suggesting panic attacks may be tied to biological rhythms, he said.
Family history plays a role too, he noted. If you have a parent or sibling with panic attacks, you have four to eight times the normal risk of getting them as well.
In laboratory experiments, researchers have shown that panic attacks can be induced by sodium lactate or carbon dioxide, which change the acid-base balance in the brain, triggering shortness of breath, one of the hallmarks of panic attacks.
And panic attacks respond extremely well to medications such as Paxil, a type of antidepressant known as a selective serotonin reuptake inhibitor, or SSRI, which boosts the efficacy of serotonin.
