I've got an oximeter at home because my grandma uses oxygen therapy, and I've noticed something about my grandpa's oxygen levels. When he's lying down or asleep, his oxygen level is usually around 92-95, mostly hovering between 93 and 94, but when he's sitting up, it goes up to 97 or 98. Is this something normal, or should I be worried? He's 70, and he doesn't have any breathing problems.