While one person may be severely unwell at a high altitude, another person at the same altitude may not be affected at all.
This is because the experience of altitude sickness and the altitude at which it occurs depends on:
- how sensitive the individual is to changes in atmospheric pressure
- how quickly they reached the high altitude
- the amount of time they spend at high altitude
Symptoms of mild altitude sickness
The symptoms of mild altitude sickness include:
- headache
- nausea
- dizziness
- tiredness
- loss of appetite
- upset stomach
- feeling unsteady
- shortness of breath
- increased heart rate
- difficulty sleeping
- generally feeling unwell
The symptoms are usually worse at night.
If you have mild altitude sickness, you can continue with normal activities. For example, if you are trekking or climbing, you can continue to climb at a steady pace.
Symptoms usually develop between 12 and 24 hours of being at altitude and begin to ease after 48 hours, as the body starts to acclimatise (get used to the changes in atmospheric pressure).
Symptoms of moderate altitude sickness
The symptoms of moderate altitude sickness include:
- severe headache
- nausea and vomiting
- increased shortness of breath
- lack of co-ordination
You will find normal activities difficult and symptoms can only be relieved by taking specialist medications and descending to a lower altitude. See treatment of altitude sickness for more information.
A good way to test whether someone has moderate altitude sickness is to ask them to walk heel to toe in a straight line. If they have co-ordination problems and cannot walk in a straight line, they should descend to a lower altitude immediately.
Symptoms of severe altitude sickness
The symptoms of severe altitude sickness include:
- worsening of the symptoms above
- a persistent, irritable cough
- breathlessness (even when resting)
- bubbling sound in the chest (caused by fluid in the lungs)
- coughing up pink frothy liquid
- clumsiness and difficulty walking
- irrational behaviour
- double vision
- convulsions (fits)
- drowsiness
- confusion (caused by swelling of the brain or fluid on the brain)
Severe altitude sickness is a medical emergency. Someone with severe altitude sickness should immediately descend by at least 600m (2,000 feet).
