I wake. The sweat-drenched sleeping bag is twisted like a tourniquet around my torso. I grope for my headlamp, switch it on, check the time, find my notepad, and pencil in: "Night 10, 23:35, 13.6% O2, 18,200 ft, can't breathe, hellish headache."
I take a swallow from my water bottle, force myself to take another, kick off the sleeping ba apnea, with fatigue, dizziness, and violent bouts of nausea still left to look forward to. All these symptoms may pass, or they may not; AMS is a fickle torturer. And there's only one sure cure: descent. It's the middle of the night and I am loath to lose altitude, but my body is clearly telling me that I'm not yet capable of sleeping at 18,200. No sleep tonight and tomorrow I'll feel hollow-headed, agitated, buzzy—the perfect mental malaise for screwing up.
I reluctantly swing my feet out of my sleeping bag, open the door, step out of the room, and instantly plunge 11,000 feet.