Usually striking at around 8,000 feet in altitude, AMS (or hypoxia) is your body's way of coping with the reduced oxygen and humidity of high altitudes. Among the symptoms are headaches, shortness of breath, loss of appetite, nausea, insomnia, lethargy, and fatigue. Some complain of temporary weight gain or swelling in the face, hands, and feet.

If your AMS is severe, you should stop ascending; you will recover in a few days. If the AMS is mild, a quick descent will end the suffering immediately.

You can reduce the effect of high altitude by being in top condition. If you smoke or suffer from heart or lung ailments, consult your physician. Alcohol and certain drugs will intensify the symptoms.

A gradual ascent with a couple of days of acclimation is best, if you have the time. On the way up, eat light, nutritious meals and drink plenty of water. A spicy, high-carbohydrate diet may mitigate the effects of low oxygen and encourage you to drink more.

Some general tips include:

• When in thin air don't overdo physical activities.
• Wear protective clothing and sunscreen for protection from the sun.
• Headache, fatigue, and nausea can be symptoms of altitude sickness.
• Extreme elevations can be dangerous to persons with heart conditions and other physical impairments. Even healthy persons are normally winded by the slightest exertion at high elevations.

You can prevent or diminish altitude sickness if you follow these tips:

• Rest up. Get at least two eight-hour nights of sleep, and make sure that you've hydrated before starting. You can also acclimate by camping near the trailhead.
• Don't race. Climb slower than your normal walking pace. If you need to rest after ascending only 20 yards, you're flirting with exhaustion and need to slow down a bit.
• When your legs start to get heavy and you feel nauseous, take a deep breath, then force air out through pursed lips like you're blowing out a candle. Do this three or four times a minute. Vigorous respiration pushes more oxygen from the lungs into the bloodstream.
• Some studies show that the herbal remedy ginkgo biloba helps increase oxygen uptake. Drugs that contain acetazolamide (such as Diamox) can prevent or alleviate some forms of altitude sickness, but be aware that there may be side effects such as numbness and frequent urination. See a doctor for a prescription and dosage information.
• Altitude sickness typically starts with nausea, lethargy, headache, irritability, and/or loss of appetite. Take immediate action. Slow your pace, hydrate, practice pressure breathing, or, just take a rest day. If your condition doesn't improve, there's one simple, surefire solution—descend.

Some of this information was borrowed from Backpacker Magazine, September 2006.