You wake up, and before your feet even hit the floor, you feel it—a dull, throbbing pain wrapping around your head. It’s not how anyone wants to start their day. You might reach for a glass of water, pop a couple of painkillers, and blame it on stress, dehydration, or maybe that extra cup of coffee yesterday. But what if the real cause isn't what you did during the day, but what happened while you were asleep?