A "Physical Ailment" that Is Commonplace in Japan and South Korea but a Cause for Concern Overseas, According to a Professor at Tsukuba University, Is "Abnormal for humans."

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How many hours of sleep per day is ideal? Novelist Jin Mayama, who interviewed Professor Masashi Yanagisawa of the University of Tsukuba, a leading expert in sleep science, says there's a simple way to tell if you're getting enough sleep. (Part 2)