Blood pressure drops about 5 points when i stand ,lightheadness and chest pain had heart,lungs checked out and blood work, all normal.what is wrong ?

Orthostatic changes: You may have orthostatic hypotension, essentially a drop in blood pressure with standing, due to a delay in the venous return from your legs to the heart. It is a very common problem in young people and has no health consequences. You have to keep yourself very well hydrated, stand up slowly and do 20-30 sec of calf muscle exercises before standing. It should correct the problem.