They had warned us about the altitude sickness, but I had assured myself that my strapping twenty-eight year old physique and mental acuteness could overcome something as trivial as natural response. Turns out, not so much.
My head was throbbing like I had just survived a Skrillex concert having been duct tapped directly to a two story subwoofer. Rising to over 11,000 feet (about 3500 meters) Lhasa is one of the highest cities in the world. If you're not from there, then you'll quickly notice the drop in partial pressure of oxygen. There isn't really less oxygen, but since there's less pressure in the atmosphere, it's not as tightly bound in the air. Imagine that instead of drinking water from a cup you poured it on the floor and like the animal you are you're licking it up. There's the same amount of water, it's just not as neatly compact as at sea level. This means you're drawing in significantly less air in Lhasa.
The result is a feeling of being hungover after a night when the next morning you look at the bottles strewn about the living room and wonder how you're still alive. Heahache, dizziness, aching muscles, and a gut punch of nausea are all common symptoms. I was feeling all of it, as were the rest of the people in my tour group and when we checked into our hotel at two in the afternoon more than a few people went straight to bed (or broke into the canisters of oxygen, which were available for $12 in the mini-bars).