Most cases of Lyme disease resolve with a 10-to-21-day course of antibiotics, usually doxycycline, amoxicillin, or cefuroxime. But not everyone who develops this tick-borne disease knows they have it or gets treated. And a small group of people who have it and get treated still develop debilitating symptoms that linger for months.

About 10 to 15 percent of people who’ve been treated have a set of symptoms that include body aches, mental fog and deep, persistent fatigue — what many people call “chronic Lyme disease.” The, Centers for Disease Control and Prevention (CDC) doesn’t recognize that term. The agency calls it post-treatment Lyme disease syndrome, and says it applies only if you had a confirmed case of Lyme disease and were treated with the recommended course of antibiotics.

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Most doctors who use the term “chronic Lyme disease” believe the Lyme infection is still active. But the CDC says the symptoms are probably the result of ongoing inflammation. The original infection may have harmed the body’s tissues, the agency says, and altered the immune system so that it is now attacking the body’s own cells by mistake.

If you feel lousy despite treatment

If you’ve finished your full course of antibiotics for Lyme disease and are hit by this wave of symptoms, see your doctor. The condition usually clears up, but it can drag on for six months or longer.

Since the symptoms are likely caused by inflammation rather than an infection, your doctor may want to treat the symptoms in much the same way as he would treat symptoms caused by chronic fatigue syndrome, according to the CDC. It also recommends following a healthy diet and getting plenty of rest as you heal. You might want to keep a health diary to track your symptoms, diet, exercise and sleep patterns, so you can discuss them with your doctor and look for patterns.

Some people with “chronic Lyme disease” symptoms seek out so-called “Lyme-literate physicians” who are willing to prescribe courses of oral or even intravenous antibiotics for six months or more. But the CDC, along with most researchers, feels this long-term therapy is useless and possibly dangerous.

Why? Four recent studies by federal health agencies found that taking antibiotics for up to six months was no more effective over the long run than a placebo, or fake pill, at improving “brain fog” or other symptoms attributed to chronic Lyme disease. In addition, for some people in the studies, side effects of the antibiotics caused serious and potentially life-threatening health problems, including blood clots.

Long-term intravenous (IV) antibiotic therapy can also lead to dangerous infections at the catheter site. In fact, a 30-year-old woman died after developing blood poisoning from such an infection. She had undergone 27 months of IV antibiotic therapy for chronic Lyme disease, even though lab tests had found no evidence of Lyme disease bacteria, according to an article in Clinical Infectious Diseases. “The use of prolonged high-dose IV antimicrobial therapy…was, in our opinion, unwarranted and ultimately led to her death,” wrote the Mayo Clinic physicians who tried to save her life. An autopsy showed no evidence that she ever had Lyme disease.

What about alternative therapies? Infectious disease experts warn that ozone, hyperbaric oxygen therapy and other costly and unapproved alternative treatments do not work for Lyme disease.

Related: 6 Ways to Treat Lyme Disease

When you should get antibiotics for symptoms of Lyme disease after treatment

The CDC and infectious disease associations agree that there are times when you do need short-term antibiotics for chronic health problems caused by Lyme disease, even if you have already been treated for it.

These late-stage Lyme disease problems are much more likely to crop up if you had Lyme disease and weren’t treated for it, but in rare cases they can appear even if you’ve been treated for it with antibiotics. This means some Lyme disease bacteria managed to escape and hide somewhere in your body, quietly doing damage that will flare up months or even years later. Here are some of the symptoms to watch for:

Unexplained knee arthritis. Some 10 to 60 percent of people with untreated Lyme disease develop arthritis and joint pain within a few weeks or months after exposure, according to different reports. Doctors often use both the ELISA test (which looks for antibodies that signal the infection) and the Western immunoblot test (to confirm the results of the ELISA test) to diagnose Lyme arthritis, as it’s called. If these tests are inconclusive, they may be combined with another test known as a polymerase chain reaction (PCR), which can detect Lyme disease bacteria’s DNA in fluid drawn from an infected joint.

Skin sores on the feet and hands. Known as acrodermatitis chronica, these sores are a light bluish-red and marked by a doughy swelling. The sores can be painful and cause skin atrophy, sometimes called “cigarette paper skin.” The condition doesn’t go away by itself, so it’s usually treated with antibiotics.

Unexplained migraines, dizziness, and sudden difficulty picking up objects or walking steadily. In very rare cases of late Lyme disease, there may be an active infection of the spinal column by Lyme disease bacteria. Lumbar testing (a spinal tap) can reveal the presence of the germs.

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Sari Harrar is an award-winning health, medicine and science journalist whose work appears in Dr. Oz The Good Life magazine, Good Housekeeping, O--Oprah Magazine, Organic Gardening and other publications.