There are a few circumstances that can cause low blood pressure. Second, unusually hot weather can cause blood pressure to drop. Third, crash diets often result in low pressure. If someone is on high blood pressure medication or has heart problems, the blood pressure drop can be even more significant. The treatment for low BP is to drink lots of fluids and to eat regularly.
Sport drinks are especially good.
Often when you replace lost fluids your blood pressure will return to normal. The sugar in these drinks will speed fluid into your cells, and the salt will help it stay there. Of course, plain water will also work wonders. If you repeatedly feel faint and light-headed during the day check with your doctor, says Debra R. Judelson, M.D., senior partner with the Cardiovascular Medical Group of Southern California in Beverly Hills, fellow of the American College of Cardiology and president of the American Medical Women's Association. Also see your doctor if you are actually losing consciousness upon standing or if you repeatedly feel light-headed , tired or weak along with signs of internal bleeding such as dark stools, she says.