Headache and nosebleeds are common phenomena when you first arrive at the plateau, and they are typical symptoms of altitude sickness. First, because of the low air density, low air pressure and higher internal pressure than external pressure, some thin-walled blood vessels under the nasal mucosa rupture and cause headache and bleeding. Second, the plateau area is particularly dry because of the large temperature difference between day and night and the low relative humidity of the air during the day. The nasal cavity is easy to lose water, and it is also easy to cause blood vessels in the nasal cavity to rupture and bleed.
It doesn't matter, drink more water and exercise less. Get used to it in a few days.