The more yellowish your pee is, the more dehydrated you are.. You lose a lot of water during the night because of sweating, breathing etc. Hence the dark yellow pee in the morning.. Keep an eye on how yellow your pee is, it should only have a tinge of yellowness to it. Any darker, and you are at risk of dehydration.. Whenever you go to the bathroom, always get in the habit of checking the color of your urine, if it is too yellowish, drink some water. . Otherwise you risk getting headaches, organ damage, migranes, lethargy, dizzy, rapid heartbeat, etc.. If it stays yellow and smelly, and doesn't change after a few days, see your doctor.