Even if you're not an extreme mountain-climber, altitude sickness can be an insidious threat. I learned this firsthand not too long ago on a hiking trail in the mountains above June Lake, California. Elevation at the trailhead was about 7,700 feet, but as I hiked the elevation rose to roughly 9,000 feet. I was carrying a light pack and moving at a moderate pace, but soon began to feel strangely nauseous and dizzy with a headache. My father-in-law, an experienced climber, recognized this as the early stages of acute mountain sickness (AMS).
In the situation above, I was able to take more frequent breaks and watch for worsening symptoms. Fortunately, the symptoms plateaued as I reached the top of the trail, and diminished as I hiked back down the mountain. But left unchecked, altitude sickness can rapidly develop into severe and even life-threatening conditions: high altitude pulmonary edema (HAPE) and high altitude cerebral edema (HACE). It's essential to know the warning signs to avoid danger.
The following infographic from Worlds Ultimate explains some of the basics of altitude sickness, including symptoms of AMS, HAPE, and HACE. Click here to download the full-size graphic.
For more information on prevention and treatment of altitude sickness, check out the following articles: