Three years ago, Andrea Vanek was studying to be an arts and crafts teacher when spells of dizziness and heart palpitations suddenly started to make it impossible for her to even take short walks.
After seeing a succession of doctors she was diagnosed with long COVID and even now spends most of her days in the small living room of her third-floor Vienna apartment, sitting on the windowsill to observe the world outside.
"I can't plan anything because I just don't know how long this illness will last," the 33-year-old Austrian told AFP.
The first cases of COVID-19 were detected in China in December 2019, sparking a global pandemic and more than seven million reported deaths to date, according to the World Health Organization.
But millions more have been affected by long COVID, in which some people struggle to recover from the acute phase of COVID-19, suffering symptoms including tiredness, brain fog and shortness of breath.
Vanek tries to be careful not to exert herself to avoid another "crash", which for her is marked by debilitating muscle weakness and can last for months, making it hard to even open a bottle of water.
"We know that long COVID is a big problem," said Anita Jain, from the WHO's Health Emergencies Programme.
About six percent of people infected by coronavirus develop long COVID, according to the global health body, which has recorded some 777 million COVID cases to date.
Whereas the rates of long COVID after an initial infection are declining, reinfection increases the risk, Jain added.
'EVERYTHING HURTS'
Chantal Britt, who lives in Bern, Switzerland, contracted COVID in March 2020. Long COVID, she said, has turned her "life upside down" and forced her to "reinvent" herself.
"I was really an early bird.... Now I take two hours to get up in the morning at least because everything hurts," the 56-year-old former marathon runner explained.
"I'm not even hoping anymore that I'm well in the morning but I'm still kind of surprised how old and how broken I feel."
About 15 percent of those who have long COVID have persistent symptoms for more than one year, according to the WHO, while women tend to have a higher risk than men of developing the condition.
Britt, who says she used to be a "workaholic", now works part-time as a university researcher on long COVID and other topics.
She lost her job in communications in 2022 after she asked to reduce her work hours.
She misses doing sports, which used to be like "therapy" for her, and now has to plan her daily activities more, such as thinking of places where she can sit down and rest when she goes shopping.
A lack of understanding by those around her also make it more difficult.
"It's an invisible disease.... which connects to all the stigma surrounding it," she said.
"Even the people who are really severely affected, who are at home, in a dark room, who can't be touched anymore, any noise will drive them into a crash, they don't look sick," she said.
FALL 'THROUGH THE CRACKS'
The WHO's Jain said it can be difficult for healthcare providers to give a diagnosis and wider recognition of the condition is crucial.
More than 200 symptoms have been listed alongside common ones such as fatigue, shortness of breath and cognitive dysfunction.
"Now a lot of the focus is on helping patients, helping clinicians with the tools to accurately diagnose long COVID, detect it early," she said.
Patients like Vanek also struggle financially. She has filed two court cases to get more support but both are yet to be heard.
She said the less than 800 euros ($840) she gets in support cannot cover her expenses, which include high medical bills for the host of pills she needs to keep her symptoms in check.
"It's very difficult for students who get long COVID. We fall right through the cracks" of the social system, unable to start working, she said.
Britt also wants more targeted research into post-infectious conditions like long COVID.
"We have to understand them better because there will be another pandemic and we will be as clueless as ever," she said.