Life force, life energy, or the essence of humanity.
Someone being injured and losing blood can represent a situation in your real life where you feel someone is in a weakened state.
You bleeding can mean you are feeling weakened or tired (emotionally, mentally, or physically), or you feel something is sapping your energy or time or attention.
Bleeding as a result of someone else injuring you can mean you are feeling threatened (emotionally, mentally, or physically) in real life—or you may be having a Toxic Dream.