Sinus infections,polyps,broke nose,pinch nerve,cancer.this is just a list of what could cause it.
Well, first maybe your head is in the refrigerator too much, watch your diet. It could be from an injury maybe even slight. Perhaps you changed your sleeping position, but most likely it is a nerve problem. It should clear up, give it a few days if it doesn't see your Doctor.
Serious question: Are you a cocaine user? Cocaine can rupture the capillaries in the nose, leading to poor circulation.