Hydration and diet. Some people become lightheaded when changing to standing from a sitting or laying position. Move so slowly to let your body adjust to blood moving away from your head. Drinking plenty of fluids and maintaining a well balanced diet are helpful in preventing lightheaded feelings. If you are still noticing these episodes, see your doctor to have the problem investigated further.
Doctor can evaluate. An normal, healthy person who gets light-headed when getting up from lying or sitting, or who feels faint sometimes, especially on hot days, may have a problem of not enough blood returning to his head fast enough. The blood pressure may be normal or a bit low. After a doctor's exam to rule out medical problems, a person can try taking 3 ounces of extra water each hour, plus a bit of salty snacks.