Altitude sickness is caused when travellers ascend to higher altitudes too quickly without allowing their bodies sufficient time to get accustomed to the atmospheric changes caused by a change in altitude. You are unlikely to experience altitude sickness if you take some basic preventive measures, such as allocating 2-3 days to become accustomed to Leh’s environment before hiking further. Increase the altitude by not more than 500 m a day; have plenty of water to avoid dehydration.