If you aren't used to higher altitudes, you may experience:

Shortness of breath
Headache
Nausea and dizziness
Loss of appetite
Fatigue
Sleep disturbances

Fatigue

Though altitude sickness tends to occur at elevations over 7,000 feet due to the decreased oxygen saturation of the blood, fast ascent or particularly strenuous activity can cause altitude sickness at lower elevations. The symptoms usually start 12 to 24 hours after arriving at higher altitudes and decrease over the course of the course of the next couple of days as the body acclimatizes.

The best way to avoid altitude sickness or the negative effects of higher altitude is to take the time to allow your body to get used to the change in barometric pressure. If you are camping, don't set out to do vigorous activity for the first day or two. If you are hiking, start slow and listen to your body as you climb. If you begin to experience symptoms of altitude sickness, slow down or stop, and, if necessary, descend slowly from the mountain.

If anyone in your family begins to experience more severe symptoms, such as nosebleeds, loss of consciousness, loss of bladder and colon control, coordination problems, coughing up bloody sputum, or swelling of the face, hands and limbs, seek medical help immediately.