If 2.6 billion people were suffering from an illness, you’d think we’d all be more familiar with it. That figure represents 33.7% of the population of the world, after all. It also represents the share of that population that will at some point experience an anxiety disorder, according to the National Institutes of Health.

For those billions, the experience of clinical anxiety can range from a persistent fretfulness, distractedness and a sort of whole-body clenching, to the paralytic crisis of a full-blown panic attack. All of it feels lousy; all of it is a state you race to escape — which typically only makes it worse. But all of it, happily, is diagnosable, controllable and ultimately treatable. The key is recognizing if your anxiety rises to the level of a clinical condition, and if it does, what to do about it.

Anxiety may, by definition, feel bad, but that doesn’t mean it therefore is bad. It’s a menacing world out there, and your brain needs a way to grab your attention when you’re stumbling into danger. The job of doing that is actually handled by two brain regions: the amygdala, situated deep in the brain’s basement, and the higher, more complex cerebral cortex.

As befits its humble location, the amygdala processes very basic emotions — fear, anger, guilt, envy — and handles them quickly and unthinkingly. The fear you experience from a menacing stranger and the fear you experience from a scary movie set off the same amygdala alarms, and do it within 20 milliseconds — a very good thing if the danger is real. The job of determining whether it is or not goes to the cerebral cortex, which sorts things through more coolly and either responds to the threat or shuts down the siren the amygdala has set off.

Sometimes, however, the alarm gets stuck. The cerebral cortex can get flummoxed trying to sort real risks from exaggerated ones: Doorknobs do carry germs, so how do you know the one you touched didn’t have something deadly? People do suffer social humiliation at parties or while giving speeches; how do you know you won’t be one of them?

The most common recognized anxiety disorders include general anxiety disorder, agoraphobia (or fear of being in public situations you can’t escape), social anxiety disorder, post-traumatic stress disorder (PTSD), specific phobias, obsessive compulsive disorder (OCD) and separation anxiety disorder. There is no blood test or brain scan that can conclusively diagnose any of them, but here are four signs that may point to trouble.

You have a high level of distress

Anxiety is a question of degree. It’s one thing to be jittery before an important test or presentation or to worry about your health when an epidemic is in the news. And if you have a particular sensitivity — flying, dentists, working the room at a crowded party — you’re going to be tense as one of those situations approaches. If the tension consumes your day, however, if it crowds out other thoughts or if the psychic pain goes from troubling to severe, that’s another matter.

“Anxiety will prevent people from sleeping; they’ll find themselves crying over it,” says psychologist Golda Ginsburg, professor of psychiatry at the University of Connecticut School of Medicine and a specialist in child and adolescent mental health. “There are students who will vomit in the days leading up to a test.”

In some cases, the emotions become so severe they lead to a panic attack, a sort of weaponized anxiety that hits fast and hard and includes such symptoms as dizziness, rapid heart rate, depersonalization or out-of-body experience and a fear of losing control or dying. “If you suddenly have to slam on your brakes and swerve to avoid a collision, that pounding heart and rapid breath you feel for a few minutes after is a form of panic attack,” says psychologist Anne Marie Albano, director of Columbia University’s Clinic for Anxiety and Related Disorders. “In the context of a disorder, however, you might start to feel the same thing the moment you walk into the office or a party.”

Your panic is persistent

An anxious brain, like a non-anxious brain, is always learning. But the anxious brain sometimes learns the wrong things and has an awfully hard time unlearning them. Once you’ve decided that people at parties are probably judging you, your brain may lock that lesson in and pretty soon generalize it to any social encounter. Ditto an obsessive-compulsive fear of disease or a panic over separation or loss. Sometimes, especially in the case of OCD, it takes just a single traumatic event — a genuinely embarrassing social moment, say, or a legitimate medical scare — for the brain to establish a fixed fear. Left untreated, those anxieties can go on for months and years.

You avoid things because of your fears

We all avoid things we fear or dislike: you could go your whole life without roller coasters or cilantro or horror movies. But they don’t really affect your life. Anxieties start to strip away the things that do. “You may dread getting a medical test because of what you could learn,” says Albano. “But if you’re avoiding going to your doctor at all because of it, that’s a problem.”

People with an airplane phobia may, similarly, limit their travel to only places they can drive. People with big dreams may sometimes settle for smaller ones because their anxiety holds them back. “I know people who went to law school and wanted to pursue a career in criminal law but were afraid to be in front of a courtroom,” says Albano. “So they push documents in a law firm instead.”

Your worries interfere with your day-to-day life

Ultimately, an anxiety disorder may become so severe that the basic business of living becomes compromised. People suffering from OCD may need hours to get out of the house in the morning because the pillows on the bed aren’t arranged properly. Schoolwork and job performance may suffer because perfectionism makes it impossible to complete a project or because social anxiety makes it impossible to talk to classmates or colleagues. Things become worse when emotional symptoms lead to physical ones such as headaches, loss of appetite and sleeplessness. “The question I ask first is, ‘Is your anxiety impairing your functioning?'” says Goldberg.

Anxiety responds well to professional care. Treatment may include psychotropic medications like Zoloft or Prozac, which can at least lower the voltage of the pain. That may make it easier to embrace and practice the techniques of cognitive behavioral therapy, in which people learn to talk back to their anxiety, reframe their fears to something less extreme, and practice self-soothing techniques like mindfulness or distraction or breathing. Slow, graduated exposure to the very things people fear also helps the brain break the link between the trigger situation and the terror that follows.

No one can live a life untouched by anxiety. But with the right skills and the right help, no one needs to live one that is destroyed by it, either.

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Write to Jeffrey Kluger at jeffrey.kluger@time.com.