On the first day of climbing, the descent back to Base Camp is quick, but soon after he arrives back at camp Krakauer is struck by a severe headache and nausea that debilitates him for the rest of the day. Thinking that it is likely due to the intense radiation of the late morning sun as he was descending from Camp One, he finally goes to see Mackenzie at the medical tent when he can’t bear the pain any longer. After vomiting out the first dose of medicine, his body accepts the second and he gratefully drifts into sleep.
Krakauer notices that the oxygen level in his supplemental tank is alarmingly low, creating a more pressing problem. Fifteen minutes into his descent, he reaches the Hillary Step, a notch in the ridge that requires rappelling. However, he sees more than a dozen climbers lined up at the bottom waiting to make their way up, and climbing-custom grants them the right of way. As he waits, he asks Andy Harris to turn off the valve on his tank in order to conserve oxygen, but Harris accidentally opens it to full flow. After a brief period of relief due to increased oxygen, Krakauer begins suffocating and realizes the mistake that Harris made. He would now have to descend 250 feet without supplemental oxygen to the South Summit, where another tank was waiting for him.