But while a fan can make your sweltering bedroom feel far more bearable, experts say sleeping with it on isn’t without its downsides. The most obvious sign of this is waking up after a night of sleeping by the fan with symptoms like a sore throat, itching or sneezing. The resident sleep expert at MattressNextDay tells Metro: ‘A fan running all night progressively dries the mucosal membranes lining your nose, throat and upper airways. POLL Poll Do you think sleeping with a fan on all night is worth it during a heatwave? Use your fan to cool the room before sleep, or set a timer so it switches off after an hour.