l ascended a summit with a highness of 3964 meter above sea level last friday . about 200 meter before the summit, l was feeling terrible. l felt dizzy. l could not see clearly. l was sort of half conscious. l learned later that l was experiencing AMS or high altitude sickness. how can l prevent it from happening again?

There is a drug that can lessen & delay effects (it is a prescription which is also used for the treatment of cataracts of the eye) & other than there r some things u can do to prevent problems - but these just lessen the side effects & wo not prevent altitude sickness.

Extra hydrating, more conditioning to prevent over exertion, & acclimatizing to higher altitudes (sleeping the night before at the base of a climb) have all worked for me but l have never experienced severe altitude sickness. Most people that experience sickness r dehydrated & over exerted & u can feel quite sick. Try these & then try seeing a doctor.

Good Luck

The thing about altitude sickness is that it is not necessarily a consistent thing - one can get it on one trip & be fine the next. l hiked up Boundary Peak (13K+ ft) (high point in Nevada) in June & felt REALLY bad. In july l climbed Rainier (14K+ ft) & felt GREAT. It has a lot to do with varying blood chemistry.

A few things u could do r (to emphasize what TahoeT wrote):

1. Ascend slowly. l usually try to not do more that 3000 ft in one day (but often do up to 5000 ft in a day). By slowly ascending, it gives ur body a chance to acclimate. As TahoeT wrote, spend a night at the base of ur climb to help get used to the altitude.
2. Drink a lot of water - one loses a lot of water by just breathing in the cold, dry air of mountainous areas. Staying hydrated does seem to help with acclimatization.
3. A medication called acetazolomide (brand name Diamox) does seem to help with acclimatization. It is actually used to treat glaucoma. l have used it in the past as a sleep aid - because it helps to regulate ur breathing & eliminate the rapid breathing & stopping of breathing that happens at altitude sometimes. It is also a diuretic (it makes u pee a lot), which could also help eliminate the build up of fluid in ur lungs or brain.

BUT.sometimes u can do all of this, & u still get AMS.

From altitude.org:

It is better to prevent acute mountain sickness than to try to treat it. Ascending at a sensible rate (300m gain in altitude per day), should mean that ur body can acclimatise as u ascend & so u will be less likely to develop acute mountain sickness. However, if u need to go up more quickly, u could consider taking a drug called acetazolamide (also known as Diamox). There is now good evidence that acetazolamide reduces symptoms of acute mountain sickness in trekkers, although it does have some unusual side-effects: it makes ur hands & feet tingle, & it makes fizzy drinks taste funny.

If u do have acute mountain sickness, the best treatment is descent. Painkillers may ease the headache, but they don’t treat the condition. Acetazolamide may be helpful, especially if u need to stay at the same altitude, & resting for a day or two might give ur body time to recover. It is essential that u should NEVER go up higher if u have acute mountain sickness.

l concur with both TahoeT and Wayner. Both cover it.