What should you know about mild altitude sickness symptoms?

Symptoms often begin after reaching a higher elevation and may include [Headache](/symptoms/headache/), poor sleep, reduced appetite, light-headedness or [Nausea](/symptoms/nausea/). The problem relates to reduced available oxygen and can affect people who are otherwise fit. A headache after travel has many possible causes, including dehydration, heat or infection, so the timing and other symptoms matter. Mild symptoms should not be treated as a challenge to push through; they can worsen if ascent continues.

Stop ascending and rest at the same elevation. Drink fluids regularly, eat lightly if able, avoid alcohol and strenuous activity, and tell a travel companion how you feel. Do not ascend again until symptoms have settled. If symptoms do not improve or you are unsure of the cause, contact a clinician or arrange a [Travel Health Consultation](/treatments/occupational-and-travel-medicine/travel-health-consultation/) before further travel. Medicines for altitude illness should be discussed before use, especially with pregnancy or other health conditions.

Descend and seek urgent medical help for breathlessness at rest, a cough with frothy sputum, confusion, inability to walk straight, fainting, extreme drowsiness, repeated vomiting or symptoms that rapidly worsen. Do not leave a severely unwell person alone. These signs can indicate a dangerous altitude-related illness rather than a mild adjustment problem.

How should I plan ascent and rest days? Are my medicines or health conditions relevant? What symptoms mean I should descend, and what supplies should I carry?