Shelley Hayden of Sonoma has a case of long COVID so serious that her “brain is broken,” she said. The 54-year-old marketing coach asked not to be interrupted in conversation so she wouldn’t lose her train of thought.

Tyler Gustafson of Berkeley recovered from COVID-19 in 2020, then got hit last summer with what felt like a heart attack: deep, aching chest pain. His body tingled. His blood pressure soared. His left side grew numb, and his thinking slowed. Even his vision became distorted. Worst of all, the symptoms never let up, so the management consultant took medical leave. He was 30 years old.

Mysteriously, Gustafson has begun to recover. But Hayden still battles frequent “crashes” that leave her mentally and physically exhausted for days or weeks at a time.

Their terrifying, conflicting medical sagas — two among millions of COVID survivors with ongoing symptoms — reveal the still-murky nature of the syndrome that has mystified doctors and caused drug companies to freeze in their tracks, unsure where to direct their treatment investments.

Patients say they feel caught in the quicksand.

“The approach to caring for people with long COVID is so bad,” Hayden said. “I’ve been teaching my doctors!”

Shelley Hayden walks with her Lab, Theo, around her property in Sonoma.

Samantha Laurey/The Chronicle

Recognizing the need to wrestle the problem to the ground faster, President Biden announced on April 5 a National Research Action Plan on long COVID. It’s a public and private collaboration that will build on Recover, a $1.15 billion initiative from the National Institutes of Health to coordinate long COVID research at sites across the country, including UCSF and Stanford.

In the two years since patients and doctors identified long COVID, researchers around the world have scanned, poked and peered at thousands of people, hoping to uncover anything that might lead to a cure for the persistent symptoms ranging from exhaustion and brain fog to racing heartbeats and loss of smell. They believe that roughly a third of unvaccinated COVID survivors suffer lingering symptoms, and about half that many patients who were vaccinated.

Scientists are gradually discovering more about the syndrome, said Dr. Steven Deeks, co-principal investigator with UCSF’s research study LIINC, or Long-term Impact of Infection with Novel Coronavirus. LIINC alone has published 18 papers, including a small new one suggesting the COVID drug Paxlovid can ease persistent symptoms.

Researchers point to three likely causes of long COVID: bits of virus that remain hidden in the body, persistent inflammation caused by the coronavirus, and autoimmunity — when the body’s own immune system turns on itself.

These, in turn, wreak havoc in four main ways, Deeks told state lawmakers at a hearing in March. They cause neurological symptoms like confusion, debilitating fatigue, cardiovascular problems, and a unique condition called POTS — postural orthostatic tachycardia syndrome — where the heart races when the sufferer stands up.