LHASA, CHINA — LHASA, China -- "Take it easy" isn't just an idle salutation here. It's a survival recommendation. The first day here government hosts are adamant -- no work, no walking, not even a lot of talking. The hotel room has a bottle of oxygen, drawn upon from a plastic tube through one's nostril. At night, a doctor comes by to take your blood pressure and offer some special Chinese herbs. The source of all the fuss is a much dreaded and somewhat common illness among visitors to Tibet, high altitude sickness. Put simply, humans need time to acclimate to the reduced oxygen at higher altitudes, particularly altitudes higher than 10,000 feet. Before acclimation, various symptoms can occur, the most common being headache, nausea, tiredness, short breath and insomnia. The symptoms usually go away quickly. However, severe reactions can progress to pulmonary and cerebral edema and ultimately death. The best way to avoid problems is to ascend to high altitudes slowly -- resting several nights along the way. The worst thing is to ascend suddenly. This is precisely what most of Tibet's 20,000 foreign tourists a year do in taking a two-hour flight from Chengdu, the capital of Sichuan province. Chengdu is about 3,000 feet above sea level. Tibet is known as "the roof of the world," and its capital, Lhasa, is almost 12,000 feet high. So get ready to feel lousy upon landing at Lhasa. In truth, I felt only a little surreal at first -- perhaps a natural product of Tibet's clear, strong light and stunning scenery. But I was not prepared for all the commotion. The government cadres who accompanied me and two other foreign reporters on this rare and controlled glimpse of Tibet had been moaning about how bad they would feel here since we first met two weeks earlier in Beijing. That only increased upon arrival. Their local counterparts jumped to the task. They carried our bags. They wouldn't let us lift a finger the first few days. They couldn't inquire too much about how well we'd slept. And they repeatedly told us about all the visitors who had done too much their first days here and thus were rendered useless. With each telling, the punchline to this story grew ever more foreboding. The heedless visitors became so sick they had to fly out of Tibet. No, they had to be hospitalized in Lhasa for almost two weeks. Not that this isn't a very serious matter. While we were in Lhasa, I heard from a longtime foreign resident that two German tourists had just died. Worried as our hosts said they were about us, it didn't stop them from attempting on our second night to ply us with plenty of beer, Chinese wine and imported cognac. Alcohol doesn't help altitude acclimation. Sure enough, the next day one of my colleagues -- who graciously participated in the ritual toasting -- fell seriously ill and had to fly back to Chengdu. Probably no visitor is immune. I had headaches the whole week, couldn't remember things and was always tired. Sleeping was hell; every two hours I woke up with a splitting headache. The best palliatives seemed to be aspirin and drinking as much water as possible. I also didn't bathe the first few days, obeying the folklore of local cadres. Not much of this helped at the end of our trip, when we were hauled in four-wheel-drive vehicles along a narrow path through a 15,750-foot-high pass. It was a spectacular place -- very silent, except for the ringing in my ears from the aspirin I'd been taking. When I walked down the path, I felt as if I was moving under water. But the best part came after we had descended a few thousand feet. Walking seemed so easy it reminded me of pictures of astronauts jumping about in the moon's low gravity. Exhilarated, I used a rest stop to zip down the path away from my handlers, where I came upon a family of Tibetans living alone in a Shangri-La setting. No one else was in sight, and they watched the bounding approach of my large, Western figure with expressions of absolute wonder. With hand signals and smiles, we exchanged greetings as best we could. It was as though I had, indeed, descended upon them and their relatively oxygen-rich valley from the moon.