On treks above 4000m, almost everyone experiences some symptoms of mild altitude sickness, with breathlessness and fatigue linked to reduced oxygen in the blood being the most common.
Mild symptoms usually pass if you stop ascending and give your body time to ‘catch up’ with the increase in altitude. Once you have acclimatised at the altitude where you first developed symptoms, you should be able to slowly continue your ascent. Serious symptoms are a different matter – if you develop any of the symptoms described here, you should descend immediately.
Mild symptoms of AMS are experienced by many travellers above 2800m. Symptoms tend to be worse at night and include headache, dizziness, lethargy, loss of appetite, nausea, breathlessness, irritability and difficulty sleeping.
Never ignore mild symptoms of AMS – this is your body giving you an alarm call. You may develop more serious symptoms if you continue to ascend without giving your body time to adjust.
AMS can become more serious without warning and it can be fatal. Serious symptoms are caused by the accumulation of fluid in the lungs and brain, and include breathlessness at rest, a dry, irritative cough (which may progress to the production of pink, frothy sputum), severe headache, lack of coordination (typically leading to a ‘drunken walk’), confusion, irrational behaviour, vomiting and eventually unconsciousness and death.