Serious illness during travel is most commonly due to pre-existing conditions such as coronary heart disease, hypertension, diabetes or asthma. The medicines you normally take may not be readily available during your travel, so bring plenty for the entire trip. Be sure to bring mosquito repellant, sunscreen, sunglasses and wide-brimmed hats when traveling to southern U.S. destinations, tropical regions or higher elevations. Altitude sickness may occur at altitudes greater than 8,000 feet but is more common at altitudes greater than 14,000 feet. Mild symptoms, which include headache, poor appetite, sleep disturbances or just not feeling well, generally resolve on their own in a few days.
Shortness of breath is an ominous sign.
More severe illness should be treated by descent to a lower altitude. Jet lag occurs when traveling through several time zones and tends to be more severe when traveling from east to west. Symptoms include fatigue lasting several days, disorientation, irritability and disturbed sleep patterns. To adjust to the new time zone, you generally need one day for each time zone crossed. If you begin your trip overtired, stressed or hungover, it will take longer.