Although minor symptoms such as breathlessness may occur at altitudes of 1,500 metres (5,000 ft), AMS commonly occurs above 2,400 metres (8,000 ft).[1][2] It presents as a collection of nonspecific symptoms, acquired at high altitude or in low air pressure, resembling a case of "flu, carbon monoxide poisoning, or a hangover".[3] It is hard to determine who will be affected by altitude sickness, as there are no specific factors that correlate with a susceptibility to altitude sickness. However, most people can ascend to 2,400 metres (8,000 ft) without difficulty.
Altitude sickness is REALLY unpredictable from person to person. Someone I was with got altitude sickness at 1600 metres (5500 ft). She'd often been to the resort before and she'd already been there a couple of days, so we assumed she had 'flu. But no. Once she got down a few hundred metres, the symptoms stopped like switching off a light. Very weird.
If David A has altitude sickness it would makes sense to rule him out now -- the last thing they should do would be to take him further up to Mexico City. But, of course, it could be something completely different.
Although minor symptoms such as breathlessness may occur at altitudes of 1,500 metres (5,000 ft), AMS commonly occurs above 2,400 metres (8,000 ft).[1][2] It presents as a collection of nonspecific symptoms, acquired at high altitude or in low air pressure, resembling a case of "flu, carbon monoxide poisoning, or a hangover".[3] It is hard to determine who will be affected by altitude sickness, as there are no specific factors that correlate with a susceptibility to altitude sickness. However, most people can ascend to 2,400 metres (8,000 ft) without difficulty.