My mini fan has been working overtime lately, taking up a permanent spot on my nightstand so I can actually get some sleep in the heat. But despite my cool head helping me drift off, I've been waking up exhausted.My sleep tracker pointed out that rather than cycling through the sleep stages, I was getting stuck in light sleep while experiencing frequent, albeit brief, wake ups. Unrelatedly, or so I assumed, I'd started sneezing a lot.Consulting a sleep expert, she helped me find the problem: my fan wasn't just streaming cold air, it was helping dust and pollen swirl around my room. As a result, my room was an allergen tornado and my sleep was suffering.Ditching the fan didn't seem like a sensible solution. I'd simply stop sneezing and start sweating. But with the help of a few easy tips, I can have it all: good sleep, a cooler bedroom, and less sneezing.Key takeaways: At a glanceRunning your fan overnight is a popular solution to sweaty summer nightsBut fans help dust and allergens to circulate which can make allergies worseSneezing, itchy eyes and mouth breathing can all cause micro-wake ups, disrupting the quality of your sleepSo despite getting plenty of hours of rest, you wake up at fatiguedCleaning your fan, keeping the windows closed and directing the fan at the wall can minimize the problemWhy is using a fan overnight causing you to wake up with no energy?Heat is terrible for your sleep. Your body much prefers a cooler room (around 65-70°F / 18-21°C, to be precise) as a drop in temperature tells your body clock that it's time to drift off.Turning the fan on is the obvious solution, right? A constant stream of cold to keep you cool during the night.But it's not just air that gets stirred up by a fan. Dust, pollen, pet dander, and all sorts of allergens get caught in the swirl and directed towards your head. Because of this, sleeping with the fan on can often cause your allergy symptoms to worsen.Get instant access to breaking news, the hottest reviews, great deals and helpful tips.As Natalie Pennicotte-Collier, sleep therapist and sleep expert at MattressNextDay explains, you're essentially shutting yourself in a room with your allergy triggers on a continuously circulating loop.Allergy symptoms disrupt your sleep stages“Worsened allergies can keep people in lighter stages of sleep rather than deeper, restorative sleep," says Pennicotte-Collier.She explains this is because allergies cause the nasal passages to become blocked, restricting airflow so you have to breathe through your mouth."[Mouth breathing] is associated with more fragmented sleep and frequent micro-wake ups throughout the night," she says. "As a result, people may spend less time in deeper restorative sleep stages and wake up feeling tired, even after a full night in bed.”