After hurrying Hiro out of the stadium, he was brought to the nearest hospital to receive treatment. And along the way, right after he was carried out of the tunnel, due to exhaustion and fatigue, as he closed his eyes to take some rest, subconsciously his body gave in; causing him to lose his consciousness.
After pushing himself beyond his limits, it's no wonder that his body gave in to the exhaustion and entered a state of recovery to heal his tired muscles.
And as Hiro opened his eyes after so long, he was immediately bombarded with the harsh glow of the florescent lights. Due to which his eyes became irritated which in turn caused him to close his eyes. However despite the sense of irritation he felt, he slowly tried to open his eyes.