Whenever I visit a Doctor during younger days for cough and allergic symptoms, he would always ask me to either reduce the fan speed or to sleep with the fan off. I have always wondered that time why anyone would ask me to sleep without a fan. But now, I understood the fact behind it.
Sleeping with a fan on doesn’t make you sick, but if you are prone to allergies or asthma, it can cause symptoms like cough or congestion from the circulating dust. Fans circulate air that may dry your nose and throat and excessive dryness triggers the overproduction of mucus, causing sinusitis, headache and stuffy nose.