What are the most common symptoms of altitude illness?

Many: Symptoms of altitude sickness include headache, nausea, dizziness or unsteadiness, confusion, mental status changes, shortness of breath and coughing. When at altitude, descend immediately at least 1000 feet; if no improvement, descend another 1000 feet. Symptoms of hape and hace (high altitude pulmonary edema and high altitude cerebral edema) require immediate air evacuation.

Most common: The earliest--if you are paying attention (and many, sadly, do not)--headache, loss of appetite, nausea, dizziness and insomnia. These can occur as low as 6500 feet, especially if you are active. Slowing down, letting yourself acclimate, or sleeping at a lower altitude are best. Taking Diamox (acetazolamide) speeds your body's acclimatization. If symptoms advance-to those described above--get down further fast!