Altitude sickness, also known as acute mountain sickness, is a common but dangerous negative health effect of high altitude, caused by acute exposure to low amounts of oxygen at high altitude. Altitude sickness generally occurs when you climb high altitudes too quickly. You don’t have to panic if you have altitude sickness while trekking as it is common when trekking in the high elevations of Nepal. However, it is risky if you do not respond to it on time. The common syndrome of altitude sickness is a headache, vomiting, loss of appetite, dizziness, severe headache etc.