I get headaches that get better when standing and worse when sitting or laying, why?

Headaches: its possible your headaches are because of low blood volume. in dehydration people can experience bounding pulsating headaches if there heart needs to pump harder and faster to mobilize low blood volume. I would try to drink more fluids, and seed if your headaches subside. Otherwise constant headaches not relieved needs to be checked out with a initial head CT without contrast study.