Lee Chung opened his eyes in the intensive care unit at Seoul National University Hospital three weeks after his collapse, his vision blurry and his body feeling like lead; machines beeped rhythmically around him, tubes connected to his arms, and the antiseptic smell of the hospital filled his nose as consciousness slowly returned.

A nurse noticed immediately and called for Dr. Kim. "Mr. Lee, can you hear me? Squeeze my hand if you understand."

Lee managed a weak squeeze, and within minutes, ...