Starting at 3, 000 metres and higher, the thin air at high altitudes causes acute mountain sickness (AMS), which can be fatal. The major trekking safety measure is to avoid climbing too quickly or high. Therefore, it is important to give the body enough time to adjust.
Immediately descend to a lower height and seek medical attention if you experience the earliest symptoms of a mountain sickness, which include headaches, shortness of breath, exhaustion, nausea, difficulty sleeping, swelling of the face, hands, and feet, and loss of appetite.