If one has a nose bleed and swallows some blood is that consider being over an a lav of Kares bishogage or the din only applies if it was other blood.
There is no problem with swallowing such blood. Essentially swallowing human blood is not included in the prohibition of not eating blood. However since it looks like like eating forbidden blood it is maris ayin and not allowed, but if the blood has not left the person’s body, it does not have an appearance of being from an animal etc. and therefore permitted.
Shulchan Aruch Y:D 66-10