How much blood? Was it bright red?
Has it happened before?
Has is happened since?
It does not sound serious. You may break some small blood vessels in your nose at night. The heat in the winter is very drying on the nose vessels causing them to be quite fragile, sometimes breaking easily. IAs we age the vessels also become more fragile. If you are taking aspirin or a blood thinner this will add to the problem.
I suggest you use a humidifier in your bedroom and keep the inside of your nose lubricated (a little Vaseline will do)
If the bleeding gets worse or more often see a doctor. Also make sure the blood is NOT being coughed up from your lung.
Even if it is cool in the room, it cold still be dry.
A humidifer would still help the air in the entire house.
Hope this helps.