Assessment of psychotic symptoms in individuals exposed to very high or extreme altitude: a field study by Hüfner, K, Caramazza, F, Stawinoga, AE, Pircher Nöckler, ER, Fusar-Poli, P, Bhandari, SS, Basnyat, B, Brodmann Maeder, M, Strapazzon, G, Tomazin, I, Sperner-Unterweger, B, Brugger, H