Sometimes, when it's quiet, you can hear what you think is you breathing. However, this breathing sound isn't yours. You see, there are these creatures called "Breathers", and they show up in absolute silence. Any sound at all, and they hide. They are thin creatures, giving them an amazing ability to hide. They have wrinkly looking skin that's surprisingly smooth to the touch, and sharp, needly teeth.
Their extreme skill at hiding gives them the ability to stalk you, explaining why you sometimes feel like you're being watched. They aren't meant to fill the room with that eerie breathing noise, though. They are meant to play the role of death. When your time has come, they strike, transporting you to your final destination. So next time you're all alone and you hear breathing, you better watch your back.