Some can barely walk they're so exhausted and their muscles so weak. Many have lost the ability to recall everyday facts or hold a conversation. Others have developed life-threatening allergies or chronic dizziness.
All have suffered months of ill-health — careers are on hold, social lives are mothballed and family life is a shadow of what it was.
GP Tanya Northridge, 40, said having Covid changed her life and said she could not walk more than 200 metres without feeling tired and dizzy
These weren't people who'd been left fighting for life on a ventilator. Some had barely any symptoms of Covid-19 infection at first, and none had to be admitted to hospital.
Yet most are now more affected by their post-Covid symptoms than when they had the infection.
The vast majority had previously been fit, young individuals. But many are now wondering if they'll ever be well again.
There is no formal definition of long Covid, although a recent paper in the BMJ defined it as symptoms lasting beyond three months.
The number affected so far in this country has already exceeded 60,000, according to initial results from the UK Covid symptom study (being run by King's College London, where people enter their symptoms via an app).
'If [long Covid] affects 10 per cent of the population [as one study suggests] and we never get better — and go from being economically active to long-term inactive and unable to work — then even if you remove the human suffering element, it is something policy-makers need to take into account,' Dr Jake Suett, 32, an anaesthetist who initiated the letter, told Good Health.
In their letter, the doctors say anyone who has Covid symptoms should be treated for the infection even if they don't get a positive test result.
They are also calling for one-stop clinics, where health professionals can gather expertise in treating persistent symptoms.
Health Secretary Matt Hancock had said such clinics were opening, but last week his predecessor Jeremy Hunt tweeted he was 'very concerned' to hear of delays to this.
There are various theories about the cause of long Covid. Danny Altmann, a professor of immunology at Imperial College London, believes the infection triggers an auto-immune reaction, where the immune system attacks parts of the body.
He cites the example of the virus chikungunya, caused by a mosquito bite. 'Some patients get better within days but others still have incredibly disabling arthritis years later, as the infection led to an attack on the joints,' he says.
Here, nine of the signatories to the letter sent to the BMJ, who all caught the infection in March, share their stories.
UNABLE TO WORK FOR MONTHS ON END
Caitriona Dynan, 49, is a consultant radiologist at Antrim Hospital, Northern Ireland. She is married to Kieran, 46, a GP, and they have a son, 11, and a daughter, eight.
Caitriona Dynan, 49, a consultant radiologist at Antrim Hospital, Northern Ireland, said her symptoms started with a horrendously sore throat
Recently my son said to me: 'Mummy you're not getting any better, are you? Are you going to die?' I was able to reassure him, but it has been a tough few months.
My symptoms started with a horrendously sore throat — like swallowing a sword — the worst kind of muscle aches and hypothermia [bad chills]. My temperature was low, down to 35, which apparently does happen in a few Covid cases.
After getting over the initial infection, for weeks afterwards I was having awful headaches and found my temperature would shoot up if I stepped outside and shoot back down once inside again. During the summer heatwave, I needed a heater by my bed as my feet and legs just would not warm up.
One day I went to stand up and went white as a sheet and dizzy — I have since been diagnosed with PoTS (postural tachycardia syndrome). It affects the autonomic nervous system, which regulates heart rate and temperature regulation.
One theory is that Covid damages the nerves. I've had other problems, too — a strange numbness in one foot. I also can't concentrate and I've needed to spend much more time in bed than I'd like.
And I've developed allergies for the first time in my life. I had a scan to check for blood clots in the lungs and I had a reaction to the contrast dye they use — which is very rare. My eyelids and lips swelled up and I had to go to A&E for high-dose antihistamines.
I haven't been able to give the kids as much attention as I would like and really miss my job.
I signed the letter, as I was concerned by reports that patients with long Covid symptoms were having them dismissed. We need to spread awareness that it's a real problem for many who, I'm sure like me, wish this could be over.
BREATHLESS JUST DOING THE SHOPPING
Jake Suett, 32, is an anaesthetist at Queen Elizabeth Hospital in King's Lynn.
Jake Suett, 32, an anaesthetist at Queen Elizabeth Hospital in King's Lynn, said he gets so breathless he needs to go slowly around the shop
I used to go to the gym three or four times a week. Now I have to plan how I'm going to manage to get round Sainsbury's.
I get so breathless I have to bring my car to the front door and need to go slowly round the shop. I'd been working with patients with Covid so it wasn't a surprise when I started to feel a cold coming on.
By day ten of the illness I was lying on my stomach gasping for breath. Yet Covid and antibody tests weeks later were both negative. It didn't surprise me, as the tests were calibrated on hospital patients, who may produce more antibodies.
Months on and I'm still breathless. I get regular heart palpitations and waves of fatigue. One minute I'm OK, then it's like a click of the fingers and I feel an overwhelming need to sleep.
For the first three months I also had waves of diarrhoea — now recognised as a symptom of Covid.
I think long Covid is going to be a lasting impact of the pandemic. We must start collecting data so we can deal with it properly.
I CAN'T FEEL MY FETT ANYMORE
Nathalie MacDermott, 38, is an academic clinical lecturer at King's College London.
Nathalie MacDermott, 38, an academic clinical lecturer at King's College London, said she has been referred to a neurologist
There have been times over the past few months when I have thought: 'What is happening to me?' I have a numb sensation in my palms, and then one day in May I suddenly could not feel the soles of my feet. It was the weirdest sensation and quite scary.
It means I try not to drive. And whereas before I walked the two miles to work, now I can't walk more than 200 metres and I have constant back pain.
I've been referred to a neurologist, who thinks that I might have inflammation in my spinal cord.
I expected to get Covid at some point (in March I was working as a junior doctor in infectious diseases in a London hospital) and thought it might be unpleasant for a while, but that would be it.
In fact, I was back to work after a couple of weeks. Then in May my temperature spiked again and I developed strange pains in my feet and general joint pain. Then came the numbness.
Prior to this, when I walked, I overtook everyone; everyone now overtakes me. My muscles don't have the power that they used to.
Covid is not just mild or severe. There are also people like me, who don't go to hospital, who end up somewhere in between. We urgently need more research into that.
RANDOM FEVERS FOR MONTHS
Sarah Burns, 41, is a GP in Southampton.
When she first fell ill with Covid, Sarah Burns, 41, a GP in Southampton, was bedbound for two to three weeks
For two months earlier this year I experienced such intense fatigue that I was lying down on the sofa all day. The only way I could manage simple tasks, such as putting on a wash, was by resting in the middle.
To put this into perspective, not only was I previously managing a busy job as a GP, but I used to regularly run 10km and had a great social life. I was barely ever in.
When I first fell ill with Covid I was bedbound for two to three weeks, but after that I went back to work.
However, five weeks later, I realised I was not OK. I would have random fevers — my temperature would suddenly shoot up to 38c — on and off for 14 weeks. And for about six weeks I had heart palpitations. When I measured my heart rate, it would be 160 beats per minute at rest — normally it's 55.
I've been referred for ongoing investigations, including with a cardiologist, and I have been told it could be another six to nine months before I'm back to my former old physical strength.
I signed the letter because, as doctors, I think we have a powerful voice. But this isn't just for us; we need to raise awareness for everyone with long Covid, some of whom won't be able to navigate the system like we can.
I FELT LIKE I HAD BEEN RUN OVER
Tanya Northridge, 40, is a GP in Brixton. She lives in Sydenham, South-East London, with her husband and their two children, aged seven and four.
Dr Northridge said she fell ill in March and was back at work after just two weeks
Having Covid has changed my life. Not only am I off work, I can't walk more than 200 metres without feeling tired and dizzy.
I can't do the school run, I can't take my kids to the park, and I can't talk on the phone for long without getting a headache.
I cannot do any upright exercise. Before this, I would be constantly on the go, and running three times a week — sometimes as far as eight miles — playing tennis and coping with 12-hour days at work as well as caring for my children.
After I fell ill in March, I was back at work after two weeks and, for April and May, I felt 100 per cent better.
Then in June, I developed a painful headache and fever, which came and went. When I got a second wave a week later, my Gp referred me for chest X-rays, abdominal scans and more blood tests and a Covid antibody test, which was negative.
But back home the fatigue hit. I did not have the strength to move my arms or legs. I felt as if I had been run over and my mind was not functioning properly. One time I argued with my husband about the order the months come in — I was convinced June came before March.
In darker moments, I wondered if I might have something else, maybe a brain abscess.
When I'm feeling optimistic, I hope I will be better in 12 months. But on my pessimistic days, I get tearful and worried that it won't ever go away.
I've had patients left virtually disabled or housebound by post-viral chronic fatigue. I'm praying this doesn't happen to me.
CONCENTRATION AND MEMORY HARMED
Grace Dolman, 40, is a hepatologist (liver specialist) at Addenbrooke's Hospital in Cambridge.
Grace Dolman, 40, a hepatologist (liver specialist) at Addenbrooke's Hospital in Cambridge, returned to work in May but was exhausted
When I developed a cough in March I didn't even feel ill but was sent home from work. But by day ten I couldn't even eat without stopping for breath.
I returned to work in May but I was exhausted by the time I got to the ward. One day the physical effort of walking from ward to ward had me almost in tears.
At the end of June I had to give up work.
I'm so tired all the time that I sleep from 11pm to 7.30am and need another two-hour nap in the afternoon. I've had to stop going to the supermarket as just deciding what to buy left me exhausted.
My concentration and memory are still poor: I put milk in the cupboard. I've also developed pins and needles in my feet and fingers.
This has destroyed my confidence. My words don't come as easily, so even talking to friends is hard.
I'm off sick until the end of October. I had just qualified as a consultant and was due to find a more senior role when this happened. I feel that I've gone from being a good consultant candidate to a lame duck.
If I was a mum with kids to look after, or a carer — and there must be many in my situation — I do not know how I would cope. My heart goes out to them.
HIT BY SEVERE ALLERGIES
Dr Jenny Judge, 48, is an NHS forensic psychiatrist and mother-of-one from Epsom, Surrey.
Dr Jenny Judge, 48, is an NHS forensic psychiatrist and mother-of-one from Epsom, Surrey
I was relaxing in the bath one evening in July when I swallowed some water. Within seconds, my throat began to swell and I was struggling for breath. Fearing I could die, I jumped out of the bath and gulped down a couple of anti-histamine tablets.
Later, doctors told me it was almost certainly a severe allergic reaction to the Epsom salts I had added to the bath, and that Covid-19 had somehow sent my immune system haywire so that it was now overreacting to things it never used to. Apart from hay fever, I have never suffered with allergies.
My GP prescribed an EpiPen and referred me to an immunologist. In the meantime, I suffered a second life-threatening reaction in mid-September after eating hazelnuts — something I've done many times without any problem. Now my worry is, what else am I in danger from?
Four weeks after I got Covid-19, I felt well enough to return to work. But as soon as I did, my temperature spiked and the racing heart I'd had when ill returned.
As the weeks wore on, I developed inflamed and painful wrists, shoulders and knees, and severe swelling in my feet and hands. I could barely hold a cup of tea.
My GP put me on naproxen — an anti-inflammatory painkiller — which helped bring down the swelling, and referred me to a rheumatologist. It's thought Covid-19 may make the immune system overreact and attack healthy joint tissue, much like rheumatoid arthritis.
In June I was rushed to hospital by ambulance with vomiting and excruciating abdominal pain — like childbirth. A CT scan revealed I had an inflamed gall bladder. Yet there was no sign of gallstones, the usual trigger. Again, the evidence pointed to Covid-19.
I spent four days as an in‑patient on morphine for the pain. Meanwhile, my heart problems continue.
I've tried and failed three times to return to work. It's like my brain is in a fog and I can't process anything.
Most people don't get long Covid but we urgently need to start tracking those that do.
NEEDED CARERS FOR THREE MONTHS
Clare Rayner, 52, is a consultant occupational physician at the University of Manchester, who lives in Altrincham, Cheshire.
Clare Rayner, 52, is a consultant occupational physician at the University of Manchester, who lives in Altrincham, Cheshire
I get chest pain and am breathless if I walk even a minimal distance. I tried a bike ride, but didn't have the strength to push the pedals.
The irony is that when I developed corona-like symptoms I thought: 'Oh, good — got that out of the way.'
Just after the initial Covid I got severe diarrhoea, vomiting, breathlessness and a temperature of 38.3c. I was taken to hospital by ambulance but they decided not to keep me in.
My temperature would come and go.
I have been so weakened by all this that I needed carers to help with the basics until recently. I have underlying health conditions: a chronic infection in my spine, which is why I had to give up being a full-time clinical doctor in 2012; and Ehlers-Danlos syndrome, which affects the connective tissues, but otherwise previously managed to care for myself.
When I saw all the other signatures on the letter, I found it quite emotional. We are just the tip of the iceberg of people affected.
Suffers wild shakes and feels emotionally fragile
By Pat Hagan
Ian Frayling, 61, is a recently retired NHS genetic scientist. He lives with wife Ann, a professor of cellular immunology and immunotherapy at Cardiff University, in the Vale of Glamorgan, South Wales.
Ian Frayling, 61, is a recently retired NHS genetic scientist who lives with wife Ann, a professor of cellular immunology and immunotherapy at Cardiff University
A few weeks ago, I went shopping for new shoes when I suddenly started to shake uncontrollably. I felt completely drained of any energy. It took all my effort just to get back to the car only half a mile away.
On another occasion I tried to buy eggs at the supermarket. But as I stood in front of the shelf, I was overcome by a sudden brain 'fog' that left me incapable of deciding how many to purchase.
Such incidents have become the norm ever since I became infected with Covid-19. I went off coffee and lost my appetite, but within a couple of days the storm really hit: a fiery fever and a cough so violent that I passed out several times.
Next came the breathing problems, which left me gasping for air. Seven months later, I still haven't made a full recovery.
I have intermittent profound breathlessness — even with the slightest exertion — rapid heart rate, my muscles feeling like putty, and brain fog.
I also get nausea, irritable bowel syndrome and hypoglycemia — where I can suddenly feel my blood sugar levels plummet, leaving me weak and trembling.
Then there's the impact on mental health.
I'm not ashamed to say it has left me feeling fragile.