He probably is pretty healthy, but he's also broken so many bones and almost died a couple times doing stunts that I can't really blame him for feeling tired. I mean if i recall he's broken his ribs a couple times, his ankles, his neck, his hips and even fractured his skull once. It's actually pretty amazing he's walking around seemingly just fine when you think about it.
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http://myanimelist.net/animelist/swordz9