I did the Huayhuash circuit in Peru in 2012. This was the highest altitude I've ever been to in my life (5000m). I live at sea level in Australia, where our highest mountain is only 2228m. This was the first time in my life I've felt the affects of having less oxygen, especially whilst exercising.
Basically, I felt pretty crap - most of the time, with one particular day when I really just wanted to stop, sleep, be left behind - recognised by some as the symptom called, 'the *uck it factor'. You just can't be arsed to do anything and want to be left alone in your own personal little world of pain.
