An intensely painful stomach ache kept me awake that night. Every time I lay down, my head spun and nausea swelled in my throat. I ran from the tent to the portable toilet a handful of times. I desperately wanted to vomit. And I tried. But I couldn't. We were scheduled to have five hours of sleep that night, but I managed to get only an hour and a half. I'd felt so strong, almost invincible up to this point.