You as a space-shuttle passenger? Some points to consider from NASA's Dr. Harold Sandler:

* "Deconditioning" -- the term used by scientists to describe the weakened state of a person returning to earth from space -- is similar to that of an ardent runner who stops his/her running regimen.

* The returning space traveler, among other symptoms, has trouble regulating his heart, loses muscle mass, calcium and bone mineral, has a decreased exercise capacity and usually is dehydrated.

* Both men and women are affected by space travel, but the symptoms tend to be less severe among older persons.

* The most severe symptom after returning to earth is fainting when standing or sitting after a resting position. (Blood is pooled in the lower parts of the body as a result of gravitational pull.)

* The body's sense of balance and motion is affected by space flight ("space motion sickness"). After returning to earth, there is a change in a person's gait, he may feel nauseous or vomit after moving the head rapidly.

* The taller you are, the more you may be affected by space flight. Because gravitational forces push against the heart and draw blood away from the heart and brain, a tall person's heart has to work harder to push the blood back to the brain; it has a longer way to travel.

* All body organs and systems are affected, but the degree varies with the individual and duration of flight.

* In the past, it has taken astronauts 3 to 7 days before they stop fainting periodically and about a month before they are back to normal condition.

The training and conditioning astronauts undergo "is not practical," says Sandler, for space-shuttle passengers because of the time involved.

"We're talking about people who have other careers, such as scientists, who want to travel in space. Our tests are determining how they will react to space stress."