I don't really know. I've done this since I was 4 when I used to get nose bleeds that lasted a good while. I got them until I was an adult when a specialist cotterized(sp?) a blood vessel in my nose. I got them even then, but not as often and not as persistently.
I also put ice cold ice packs on my forehead.
I suppose you are swallowing blood that has been exposed to the air. That means it is carrying oxygenated blood. Other than being prohibited in the Bible, I don't see anything really wrong with it. When you look it up, it says that it can bring about vomiting. That never happened to me.