The majority of people who believe they have a chronic form of Lyme disease are more likely to have chronic fatigue syndrome, experts suggest.
There are around 3,000 cases of Lyme disease, caused by tick bites, in the UK each year.
Most of those who take antibiotics make a full recovery within months.
But infectious disease doctors are warning that long-term Lyme disease cases are often misdiagnosed through expensive and unvalidated tests abroad.
Dr Sarah Logan, from London's Hospital for Tropical Diseases, said: "Most people who now think they may have had Lyme disease, in fact have a syndrome that is more in keeping with chronic fatigue syndrome."
Speaking at a Science Media Centre briefing, she added: "And because there is increased awareness about it, they are testing for Lyme disease and then they are going on to various different Lyme disease forums on the internet and being told, 'Well actually the UK tests are rubbish, but you need to send it off to Germany.'
"Then they are coming back with a test that is positive and saying, 'You doctors are all wrong and I don't have chronic fatigue syndrome, I have chronic Lyme disease.'
"I think that most people who think they have got Lyme disease in the UK, probably don't."
She cited two cases she had seen where patients, believing they had chronic Lyme disease, had been taking intravenous antibiotics - one developed a Clostridium difficile infection as a result of being on the medication for more than six months. The second patient also developed a serious infection.
Dr Logan said it could be that chronic fatigue syndrome was a difficult diagnosis for doctors to give, because it could be hard for patients to get treatment and support, and because of persisting negative views of the condition.
"I think there is a bit about patients not wanting to hear it because of all those stigma reasons, and there is a little bit about GPs hoping - probably not unreasonably - and saying, 'Let's look for an alternative diagnosis because then that is something we can treat.'"
When a Lyme disease test comes back negative, patients may decide to seek testing elsewhere, she said, adding that some patients were paying up to £600 for a consultation and test that has not been validated.
Dr Matthew Dryden, a consultant microbiologist at Hampshire Hospitals NHS Foundation Trust, said he was also concerned about the issue of "chronic" Lyme disease.
"These are reported as true cases of Lyme when almost certainly they're not. The symptoms are very real but most medical tests tend to be normal which confuses both doctors and patients."
He said the focus should be improving the management and care offered to patients with chronic fatigue.
"It really needs improved research and improved management services for these patients."
What is Lyme disease?
- Lyme disease is caused by bacteria carried by some species of ticks - around 13% in the UK are believed to be infected
- It cannot be passed from person to person
- Symptoms - including the bullseye rash, fatigue and fever - usually develop around three weeks after a bite
- The majority of those who take the full three-week course of antibiotics make a full recovery
- The New Forest and the Scottish Highlands are known Lyme disease hotspots - but people should take care wherever there is long grass
- The NHS test, which is highly accurate, looks at antibodies the body produces, which can take some weeks to reach detectable levels
Source: Public Health England/NHS