Now that we're getting to warmer weather, you might be reaching for a way to cool down at night. Don't have AC? A fan is your next best friend... but be aware. According to The Sleep Advisor, as a fan moves air around the room, it causes flurries of dust and pollen to make their way into your sinuses. It can also cause dry skin. And if you sleep with your eyes partially open you could also be at a disadvantage because your eyes will obviously be completely dried out, which could cause irritation. People who sleep with a breeze directly on them may wake up with stiff or sore muscles. This is because the concentrated cool air can make muscles tense up and cramp.