Jayden Hardowar, 8, of Richmond Hill, Queens, spiked a mild fever sometime around April 23.
A pediatrician told Jayden's parents not to worry and to continue taking children's Tylenol, his father, Roup Hardowar, told ABC News on Thursday.
In three days, his fever went away, but he began feeling weak. Soon, he lost his appetite, and his pediatrician suggested Jayden drink Pedialyte over a video-conferencing call.
Roup said the family wasn't worried about coronavirus because they were following stay-at-home orders.
"He was doing fairly OK at home," Roup said. "We were confident. We weren't concerned, because we know that we've been practicing social distancing as a family."
But on April 29, while watching Pokemon on TV, Jayden called out for his mother and threw his hands up, struggling for air before going into cardiac arrest.
His 15-year-old brother, a Boy Scout, did chest compressions until the ambulance got there.
"He saved his brother's life," Roup said. "We managed to get some sort of breathing back."
Jayden received an electric shock after first responders found an irregular heartbeat. At Cohen's Children's Hospital in New Hyde Park, he was put on a ventilator in the intensive care unit for three days before the staff saw improvement.
Doctors in the U.K. first warned of the mysterious illness linked to exposure to COVID-19 in April. Cities across the country are reporting cases of the rare illness, from Boston to Washington, D.C., to Los Angeles.
An advisory issued Monday by the New York Department of Health names fever, inflammation and single- or multi-organ dysfunction among some of the symptoms of the syndrome. PIMS, the health advisory says, can feature symptoms that "overlap with Kawasaki Disease and Toxic Shock Syndrome."
Children's Hospital in Los Angeles reported three cases of PIMS, saying Thursday in a statement, "These patients tested positive for antibodies against SARS-Cov-2 virus (which causes COVID-19) but tested negative for the virus by RT-PCR," suggesting the inflammation is a "late response to a recent past infection with SARS-Cov-2."
Dr. James Schneider, the chief of pediatric critical care medicine at Cohen's Children's Medical Center, said this previous infection causes the immune system in these cases to get hyperactive.
"That overactive immune system leads to this whole systemic inflammation that leads to the cardiovascular system being compromised," Schneider said.
He added, "There’s a standard treatment for Kawasaki that we’ve known for many years now and is very effective. And so we’re treating these children with that therapy."
Jayden, too, tested negative for the virus, but positive for COVID-19 antibodies, suggesting he had been previously infected weeks or even months ago.
Today, Jayden is alert, but struggling to speak. For the first time since his hospitalization, he's allowed one visitor, which Roup said will be his mother.
"I'm so glad she gets to see him," Roup said.
He hopes his son will be home by the weekend or early next week.
"That's our hope right now," he said. "The doctor sort of alluded to that as an option. So we're looking for that." But for now, they're taking it one step at a time.
On Thursday morning, Jayden started eating again on his own -- beginning with a bowl of cereal.