You have to suppose that blood in the game is only representative of 40% of your actual blood supply, because there's not much point modelling the effects if you lose more than that. The symptoms of severe haemorrhaging fit pretty well in this regard. The thing is that the blood loss itself isn't necessarily realistic. I mean if you're gushing out like a whole bag's worth of blood in a matter of seconds, a bandage is probably not going to do it justice. In reality a lot of people would just die from lack of medical attention, even with the appropriate first aid gear. Of course Sepsis: The Video Game is not an appealing concept, so you make representative systems rather than a perfect 1:1 clone of reality.
