Symptoms of altitude sickness usually develop between 6 and 24 hours after reaching altitudes more than 3,000m (9,842 feet) above sea level.
Symptoms are similar to those of a bad hangover.
The symptoms are usually worse at night.
It's not possible to get altitude sickness in the UK because the highest mountain, Ben Nevis in Scotland, is only 1,345m.
Consider travelling with these medicines for altitude sickness:
The best way to prevent altitude sickness is to travel to altitudes above 3,000m slowly.
It usually takes a few days for the body to get used to a change in altitude.
You should also:
Acetazolamide, available from a travel clinic and, in some areas, your GP, can help prevent symptoms. It's thought to help you adjust more quickly to high altitudes.
You should begin taking the medication 1-2 days before you start to go up in altitude and continue to take it while going up.
If using acetazolamide, you should still go up gradually and follow the general prevention advice.
If you get symptoms of altitude sickness while taking acetazolamide, you should rest or go down until you feel better before going up again.
If you think you have altitude sickness:
Acetazolamide can be used to reduce the severity of your symptoms, but it won't completely hide them.
Tell your travel companions how you feel, even if your symptoms are mild – there's a danger your judgement can become clouded.
You can continue going up with care once you feel fully recovered.
If you don't feel any better after 24 hours, you should go down by at least 500m (about 1,600 feet).
Don't attempt to climb again until your symptoms have completely disappeared.
After 2-3 days, your body should have adjusted to the altitude and your symptoms should disappear.
See a doctor if your symptoms don't improve or get worse.