My father invited a friend of his to lunch today who has extensive experience trekking in high altitude regions - Karakorum is his favorite, though he also did a 250-mile (!) trek around Annapurna some years ago. He's also a medical doctor, so I was able to get some non-anecdotal advice on what to expect at the high altitudes of the Kailash pilgrimage, and how to prepare. In the sober way of a doctor, he told me that 
many people's breathing pattern changes, to what's called "periodic" or Cheyne-Stokes breathing. One might well awake in the middle of the night (not that anyone sleeps well up there) and find that one's breathing has stopped. No cause for alarm: the usual triggers for breathing related to CO2 are disrupted in these oxygen-poor climes, but the body will resume breathing as needed. Forewarned is forearmed.
Perhaps relatedly, people have vivid dreams and even hallucinations!
many people's breathing pattern changes, to what's called "periodic" or Cheyne-Stokes breathing. One might well awake in the middle of the night (not that anyone sleeps well up there) and find that one's breathing has stopped. No cause for alarm: the usual triggers for breathing related to CO2 are disrupted in these oxygen-poor climes, but the body will resume breathing as needed. Forewarned is forearmed.Perhaps relatedly, people have vivid dreams and even hallucinations!
