Haha, Sudeep, in Nepal this must be really common right? It's really high up in the mountains of the Himalaya right?

Its altitude sickness :). I always get altitude sickness when I go to the mountains >.< 

We never say mountain sickness, but we would understand haha

がんばて！ 

Dear Ivar,Aura,Shawn and Sudeep

Thank you very much for your help! :)

I got it!!

I want to say that word because I got sick (I guess it was altitude-sickness),when I climbed at Mt,FUJI !!! :) 

Hi there Sudeep! Actually I am a little bit of a knower on the subject—I don't know if the word "knower" exist in litterary english, but I think you can understand the intention of it. It does'nt exist a movie about high-altitude-climbing I have'nt seen. Newer have I heard of the expression mountain-sickness, but the other you mention altitude-sickness apears quite often, if you know what I mean. now it's up to you how you put your tounge, so to speak. 

I've heard of "sea sickness" when one is sailing in a boat on a rough body of water (I think it's usually rough water... can people get "sea sick" sailing through calm water?), but I've never heard of "mountain sickness" or "altitude sickness." That's probably because I don't live near mountains and no one where I live would say anything like that.

However, I have experienced the sensation of gradually going up in altitude (or elevation) driving through mountainous regions. I've also experienced the same sensation during the take-off and landing of an airplane flight, and that would simply be "airplane sickness" I think.

Maybe someone who lives in this kind of region in the United States would have a better answer to your question. Personally, I think if you said "mountain sickness" or "altitude sickness" I think other people who have experienced the sensation would understand you. If not, you can just explain how you're feeling and that those feelings are caused from the elevation of the mountains.