This story, and the one of Diane that Steve linked, is scary.
It illustrates that for HAPE (and also especially for HACE) that (1) the warning signs and symptoms may be subtle or missing, and (2) once someone has the ball rolling with HAPE, it can continue to roll even though they make it back to the safety of lower altitude.
The medical reasons are mysterious, but basically it is a cascade of multiple factors like fluid shifts and metabolic changes in the lungs, brain and other parts that are set off by the initial time exposed to lower oxygen. This can be reversible, or fatal. I am glad for the fortunate outcome in this case.
