Altitude sickness: what elevation can cause it?

It may occur at a lower sleeping elevation in a susceptible person, while another traveller may feel well higher up. The risk rises when someone gains sleeping altitude quickly and does not allow time to acclimatise.

Acute mountain sickness commonly presents with a new headache after ascent, together with nausea, dizziness, unusual tiredness, poor appetite, or disturbed sleep. Symptoms often develop within hours of reaching a higher elevation. Fitness does not prevent the condition, and a previous trouble-free trip does not predict every future ascent.

Stop ascending and remain at the same elevation while symptoms are mild. Rest, avoid alcohol and strenuous exertion, and do not use pain relief to justify climbing higher. If symptoms worsen or do not settle, descend to a lower elevation with another person. Before a high-altitude journey, plan gradual sleeping-height gains and discuss prevention medicines when your route allows little acclimatisation time.

Confusion, difficulty walking in a straight line, severe drowsiness, breathlessness at rest, chest tightness, blue or grey lips, or a cough producing frothy fluid can signal severe altitude illness. Begin descent immediately if it can be done safely, arrange emergency help, and use supplemental oxygen if trained support has it available. A person with these signs should not descend alone or wait for morning.

Ask whether your planned sleeping elevations allow enough acclimatisation, whether a previous episode changes your plan, and whether prevention medication is suitable for you. Mention heart or lung disease, pregnancy, sleep-related breathing problems, and all regular medicines. Also clarify which symptoms should trigger descent and where medical assistance is available on your route.