When HAPE is not recognized and treated, it can be deadly, according to Dr. Michael Yaron, professor of emergency medicine at University of Colorado.
"Usually, it's associated with alcohol," said Yaron. "The typical story is college buddies come out here and go for it, ski hard. ...One buddy is not feeling that well and goes out to dinner, gets really drunk and in the morning starts to get altitude sickness, but it feels like a hangover."
HAPE develops over 48 to 72 hours, and the skier gets sicker, but his friends are drinking and skiing and don't pay attention.
"They go out drinking without him and come home and don't notice their buddy snoring loudly and not getting up," said Yoran. "The next morning, he is dead."
As for Navratilova, HAPE came on in classic fashion after several days and was caught in time.
The Web site for Laureus Sport for Good Foundation has kept a log of the progress.
"Obviously all awoke this morning gutted to hear the sad news that Martina had had to abandon the climb," they wrote today.
"Everyone was devastated that she would not be there to summit with us and her absence in the mess tent at breakfast was felt by everyone. However, everybody was well aware that a tennis great like Martina would not have descended unless she had to."
Among other team members are British Olympic badminton star Gail Emms and German paralympian Michael Teuber.
Navratilova, who lives in Aspen, Colo., has won 18 singles Grand Slams. Navratilova was diagnosed and treated for breast cancer this year and her prognosis is excellent.