The man appeared suddenly and out of nowhere. Jeremy Windsor exchanged a few words of encouragement with a fellow alpine climber who introduced himself as Jimmy, then they slowly walked on uphill, side by side. At an altitude of over 8200m on the southeastern slope of Mount Everest, one has no desire to spend precious oxygen on small talk. For the rest of the day Windsor, an experienced American mountaineer, kept seeing his companion's silhouette a few steps behind his right shoulder. Later, during the descent, Jimmy vanished just as suddenly as he appeared hours earlier.

Only when Windsor made it to the base camp, did he realise there was no 'Jimmy' or any other companion who'd walked beside him that day.

Study of climbers' experiences conclusive of yet unknown mental condition

It is not uncommon when climbers' senses are deceived by some strange illusions at ultra-high altitudes. These can range from seeing and talking to phantom companions to food smells and car noise, or even seeing an alpine hut appearing out of nowhere. According to Katharina Hüfner, a neurologist and psychiatrist at the university clinic in Innsbruck, the account of Jeremy Windsor is typical. Together with Hermann Brugger, head researcher of the Institute of Highland Emergency Medicine in Bolzano, they investigated 83 reports by climbers from across the world.

Published by Psychological Medicine, the joint study by Eurac Research and the Medical University of Innsbruck examined descriptions of this phenomenon which included such accounts of renowned climbers like Hermann Buhl and Reinhold Messner, the detailed testimony by writer Jon Krakauer, as well as the stories told by many other climbers.

Hallucinations syndrome differs from high altitude sickness

Until now, medical science explained such hallucinations as the "third person syndrome," different from the most studied high-altitude sickness. The latter is associated with conditions such as the life-threatening cerebral oedema, or brain swelling, caused by a rapid rise in altitude, as well as dehydration and infections.

Early symptoms of acute altitude sickness are a severe headache, dizziness, or imbalance. In about a quarter of all reports studied to date, however, climbers described only signs of Psychosis without any accompanying physical symptoms. Physicians now consider these hallucinations a psychosis of a specific kind, different and independent from the classic high altitude sickness. Mr Brugger and his team named this phenomenon "an altitude-induced isolated psychosis." According to Katharina Hüfner, this mental condition usually manifests itself at altitudes of 7,000 m, yet sometimes it can also develop at a "normal Alpine" height of 4,000 m.