Blood overhaul is a very recent feature, and thus blood transfusion is not yet implemented.
It seems your character lost lot of blood volume and lot of red cells. This is not necessarily a fatal condition even though at final stages the risk is out there. Solution to this is being always hydrated to replenish the plasma. Other than that treat your character as badly wounded, stay in hideout for a day or two, maybe craft something, allow natural restoration of blood, don’t engage in combat and hope for the best. Hypovolemia will pass faster then anemia from red cells loss, as blood volume restores faster then the cells themselves. Monitor your status in the next few in game days.
I will return to implementing blood related features as soon as it’s possible for me. As a teaser I’ll say that I have darbopoetin alfa medicine in works right now (red blood cells regeneration booster) and coming soon ™.