About 1 in 22 people who survive COVID-19 go on to develop a typically lifelong disease called myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), new research

ME/CFS (formerly called "chronic fatigue syndrome") affects roughly 1 in 100 adults in the U.S. One of its main components is post-exertional malaise, in which people's symptoms suddenly worsen after physical or mental exertion. People with the condition often experience unrefreshing sleep, brain fog and orthostatic intolerance, or sudden blood-pressure dips upon standing. Doctors are still trying to understand the biological causes of this understudied condition, but as of yet, no approved treatments exist.

Notably, ME/CFS has many overlapping symptoms with long COVID, an umbrella term that describes a range of health issues that emerge or worsen after a COVID-19 infection.

"By my rough calculations it is possible that over 7 million Americans may have developed ME/CFS following COVID," Beth Pollack, a research scientist at MIT who studies ME/CFS and long COVID, told Live Science in an email.