You dodged the initial spring 2020 wave of COVID, but caught the virus during the Delta wave of fall 2021, or the initial Omicron wave the following holidays, or another Omicron spawn more recently. Months later, you find yourself feeling a little tired and … foggy.

You could be forgiven for wondering, “Do I have long COVID? Is that why I’m mentally hazy?”

Indeed, brain fog, muscle aches, and fatigue are some of the most common symptoms of the nebulous condition called long COVID, which experts think affects as many as one in five Americans who survived the relatively new virus.

They’re seemingly mild, compared to the more than 200 other potential symptoms of long COVID, like the development or worsening of cardiac ailments, autoimmune diseases, and neurological issues like a persistent feeling of “brain on fire.”

Just how likely is it that your new, post-COVID symptoms are long COVID? How long will they last? And what’s the difference between a bout of brain fog and a potentially fatal post-COVID complication?

What’s to blame for my new health issue?

They’re the questions on the minds of countless patients and doctors right now: Is my new eczema long COVID? Is my worsening diabetic glycemic control due to COVID? I feel kind of mentally foggy—am I a “long hauler”?

It’s hard to attribute a symptom to a condition like long COVID when that condition has yet to be clearly defined, experts say.

The trouble is that—for now, at least—“long COVID” can encompass everything from patients who had mild COVID and have lingering mild symptoms, to those who were hospitalized with severe COVID and continue to suffer from resulting organ damage, Dr. Alba Miranda Azola, co-director of the Post-Acute COVID-19 Team Program at Johns Hopkins University School of Medicine, told Fortune.

For those with pre-existing conditions, it’s impossible to say if such outcomes—say, a heart attack—are due to COVID, the condition, or a combination of both—and the answer might vary by person. Those who had severe COVID-19 are at greater risk for death in the year following, according to a 2021 study out of Florida that considered more than 13,000 health records. And a study published in March of this year, considering over 150,000 COVID survivors and control groups in the thousands, found that survivors were at a substantially increased risk of heart disease, which could lead to death.

What’s more, some long COVID patients have symptoms that aren’t related to the condition, or that would have occurred anyway.

When will it go away?

As far as how long “long COVID” symptoms might last, some patients do report improvement and symptoms that resolve completely in a matter of months, experts say. 

But countless others have not reported such a resolution. They may eventually recover; it’s too early to say. “We’re only two and a half years into the pandemic,” Dr. Glen Mays—the chair of the Colorado School of Public Health, as well as a professor there—told Fortune. Society has yet to truly “see what the long-term consequences are.”

Many who self-report long COVID simply have “post viral complications” that could happen after many viral and bacterial infections, such as Lyme disease and Epstein-Barr virus, Dr. Panagis Galiatsatos, an assistant professor at Johns Hopkins’ Division of Pulmonary & Critical Care Medicine, recently told Fortune.

In these cases, it will likely take someone three to six months to get back to normal. Healing from COVID can be a lot like healing from a scraped leg after a fall from a bike, he said.

“The initial impact of the scrape is gone, but the scar is going to take time to heal,” he said. “Patients who are still coughing at two months—that’s part of healing.”

Mental haze, something more serious, or both?

There’s no evidence that patients who had mild COVID symptoms and now have relatively mild long COVID symptoms are at an increased risk of mortality, Azola said.

But that doesn’t minimize the potential harm of such symptoms. For example, mental haziness could put someone at a greater risk of a car crash or an injury while operating heavy machinery.

“Brain fog—you may not think it may immediately or directly result in death, but imagine situations where if you’re not able to concentrate, think—you may be more likely to have an accident,” Dr. Bruce Y. Lee, a professor of health policy and management at the City University of New York School of Public Health, told Fortune.

Those with long COVID who are easily exhausted may not be able to get adequate exercise, which could elevate their risk for chronic disease—like obesity, high blood pressure, and type 2 diabetes—and premature death in the future, Mays said.

And then there’s the mental health impact of long COVID that can’t be ignored, he pointed out.

“There’s an epidemic of mental health problems in the U.S., partially accelerated, directly and indirectly, by the COVID pandemic,” Mays said. “That’s another pathway where long COVID can have severe adverse effects on health” by creating mental health conditions or worsening pre-existing ones.

Long COVID symptoms like depression and anxiety “can be deadly,” he said, adding that the inability to move like one used to, exercise regularly, and attend work can also lead to a “longer pathway toward health decline.”

Not inevitable

The best advice, experts say, isn’t to accept long COVID—or even COVID—as an inevitability, and to take precautions like using face masks and social distancing.

“There’s a spectrum of how people get it,” Galiatsatos said of the virus, adding that “how you catch COVID” may determine if you develop long COVID. For instance, those who vaccinate and/or treat their infection with antiviral Paxlovid may be at lower risk of developing the condition, some studies suggest.

Statistics like the CDC’s assertion that one in five U.S. adults who’ve had COVID have long COVID are generally based on surveys, with individuals self-identifying and not necessarily having been formally diagnosed.

Such questionnaires are basically asking, “Do you have any new health problems since you’ve had COVID?” Dr. Alexandra Brugler Yonts, an infectious disease specialist who runs a long COVID clinic at Children’s National Hospital in Washington, D.C., recently told Fortune.

 “Which is a challenge, because life still goes on, and people still develop health conditions.”

The takeaway: Now is not the time to throw your hands in the air and caution to the wind. COVID can be avoided—at least sometimes—long COVID isn’t inevitable.

Said Brugler Yonts: “Just because I’m probably going to get flu at another point in my life doesn’t mean I lick subway rails.”