Extreme fatigue, nausea, chest tightness, severe headaches, "brain fog" and limb pains are among the recurring symptoms described by some sufferers of Covid-19 for weeks - and even months - after their diagnosis.
They call themselves "long-haulers" and their symptoms persist long after the 14-day period that's officially said to be the average length of the illness.
There are calls for both health professionals and employers to recognise that some people will take a lot longer than two weeks to recover.
"It's the weirdest thing I've ever experienced," Helen Calder, from Liverpool, told BBC health correspondent Dominic Hughes.
Nearly four months after she and her family caught the virus, and after needing hospital treatment twice, she still experiences a relapse roughly every two weeks where she is hit by debilitating fatigue, nausea, headaches and limb pain.
Her doctors have diagnosed post viral fatigue and she says any small over-exertion while she is feeling well can set her back for days at a time.
A very brief runaround with her young daughter during a family outing left her back in bed for days afterwards, completely exhausted.
Donna McCulloch, from Winchester, was diagnosed by her GP on 23 March - she did not have a test - but says she was at her worst seven weeks later.
"The whole of April and most of May were an absolute wipe-out," she says. "Everybody was saying it was 14 days, and I just didn't get better. By week six I was panicked."
Concerned about a secondary infection, her doctors prescribed antibiotics, which she says made her feel even worse.
Donna now finally thinks she is on the mend: "I'm not where I was - but I've done everything I can to get myself get back on track."
Donna and Helen are far from alone.
Thousands of people are sharing stories of their prolonged battle with Covid-19, using hashtags and joining Facebook groups like the Long Covid Support Group, which has more than 5,200 members.
Data from the Covid Symptom Study app, downloaded more than three million times, suggests a "significant number" of people report symptoms for a month. One in 10-20 report it for longer than that, says genetic epidemiologist Prof Tim Spector, who came up with the app idea.
"When this started, everyone assumed it was like the flu, it would all be over in a week and a few people would end up in hospital and either recover or have problems," he says.
"And we now know from people logging onto the app every day that there is a significant proportion of people who have problems lasting not just the average... but over a month."
Dr Jake Suett, an intensive-care doctor in Norfolk, who was himself ill for several weeks, wrote an open letter calling on the government to push for more research into long-haul symptoms, and also to raise awareness among not only health professionals but also employers, who may see their staff off work for longer than two weeks.
"These patients may require financial help, and their employers need to have a realistic expectation for the time it will take them to recover," he wrote.
The issue has since been raised separately in parliament, and NHS England has just launched a new service to help people deal with the long-term effects of coronavirus.
The government has also announced an £8.4m study into the long-term impact on health. But Dr Suett has not yet had a response.
So what is going on?
Long-term consequences also affect some people who experience other chronic respiratory illnesses, including viral pneumonia in various forms, says Dr Michael Head, an epidemiologist at the University of Southampton.
It's difficult to pin down whether there are more or less people affected in the case of Covid-19, because existing studies into other conditions give inconsistent results. But Dr Head says the variety of its symptoms could be more unusual.
"What may well be different with Covid-19 is the sheer range of observed long-term health consequences."
The tiredness, "brain fog" and lingering loss of taste and smell that many long-haulers report has led some to ask whether the virus actually attacks the brain.
"It's not yet fully known as to how these symptoms come about, for example whether the virus has an indirect effect on the nervous system, or whether it can pass through the blood-brain barrier and affect the brain directly," says Dr Head.
"It is certainly very clear that the virus does affect many parts of the body beyond the lung."
Prof Paul Garner from the Liverpool School of Tropical Medicine is an epidemiologist who has been studying his own post-Covid19 long-haul journey since he first fell ill on 19 March.
He describes his condition now as being like Chronic Fatigue Syndrome (CFS) or ME.
He says some sufferers think their condition must be psychological, because they can't believe they are experiencing such intense symptoms for such a long time.
"They think, 'I can't be going through this, this is too strange. I must be having a mental breakdown'," he says.
"I've spoken to general practitioners who think they are undergoing a nervous breakdown. But, actually, they've just got symptoms of the disease."
Ultimately complete rest is crucial to eventual recovery, Prof Garner says - but many people will feel unable to do that, either for financial or family reasons, or both.
"If you don't give the body time to heal, it kicks you back," he says.
"Rushing back into work because you have to is more likely to make you ill again and likely to delay your recovery, and people haven't thought this through, I think."