sleeping with a fan on is extremely dangerous and most people do it every single night you thinking the breeze is keeping you cool and comfortable but it's actually launching a silent attack on your respiratory system... when you sleep with moving air directed at you, it rapidly evaporates the moisture from your mouth and nasal passages. your body reacts to this extreme dryness in panic mode producing excess mucus to try and compensate. this is why so many people wake up feeling congested with a stuffy nose or a pounding headache but it gets worse; a fan doesn't just blow air it acts as a vacuum for dust and dead skin cells shooting them directly into your sinuses for eight hours straight but here's the strangest part: sleeping with a fan can actually damage your eyes, many people sleep with their eyelids partially open without realizing it, that constant air flow dries out the surface of your cornea all night long leaving you with red and irritated eyes the moment you wake up.