Altitude sickness is unpredictable. It occurs when you travel too high too quickly, but not every time. It is, however, always serious.
You may experience altitude sickness when you rapidly increase in altitude without allowing time for your body to adjust. There is less oxygen in the air at higher elevations, and oxygen deprivation can lead to negative side effects.
If you are at a high altitude, your doctor may think you have this condition. Your doctor will ask you questions about your symptoms and examine you. To rule out other conditions, your doctor may ask if you have been drinking fluids or alcohol or using any medicines, or if you have a cold or the flu.
What are the symptoms?
Watch out for signs between six and 24 hours at altitudes of more than 3,000 m (9,840 ft) above sea level, including headache, nausea and vomiting, dizziness, tiredness, loss of appetite, and shortness of breath, which is worse at night.
Can you prevent it?
The best way is to travel slowly up to altitudes above 3,000 m and take medicines for altitude sickness with you.
What's the treatment?
If you think you have altitude sickness, stop and rest where you are. Don't go any higher for at least 24-48 hours.
If you have a headache, take painkillers, and if you feel sick, take an anti-sickness medication. If your symptoms don't improve or get worse, descend as soon as possible, and see a doctor.
If the symptoms of altitude sickness are ignored, they can lead to life-threatening high altitude cerebral oedema (HACE), swelling of the brain caused by a lack of oxygen, and high altitude pulmonary oedema (HAPE), a build-up of fluid in the lungs.
These are serious conditions and require immediate treatment.
Does a drop in temperature make you ill?
Well, yes, but not in the way you might think. A study found that exposing your skin to cold temperatures isn't what makes you susceptible to the common cold. What's more likely to make you ill is the drop in humidity linked to that drop in temperature.
As lung specialist, Ray Casciari in Orange County, California, US, says, in a low-humidity environment "your eyes tend to dry out, the mucous membranes in your nose dry out, and your lungs dry out, and you are therefore much more susceptible to bacteria and viruses".
As viruses are more likely to survive and multiply in cold than heat, you are more prone to getting sick when the weather turns cold.