When you arrive in Lhasa, usually the hotel clerk should suggest you not to take a shower at the first night. You can feel heavier panting in Lhasa, especially when you take showers. The atmosphere pressure in Lhasa is only 60% of what it is at the sea level. All the non-vacuum packing stuff will look bulgy as you see in the picture below.
It took me four days to get rid of the high-altitude illness.