There are as many different opinions for interpretation of dreams as there are people that do it. It depends on who you ask.
The mechanism of why we dream is not fully understood, by anyone. That it is a function of the subconscious is fairly well agreed upon but there are many theories as to why and how we dream.
People have different solutions with the conscious mind when presented with the same data, it is far more difficult to explain the functioning of the unconscious one. It is, however, unlikely that precognition is involved.
In this particular dream, it all depends on what you feel about blood. It can refer to love, life, disappointments or passion. Blood on the walls could be a warning from the subconscious mind. Blood on a bathroom wall could mean you have a highly charged emotional issue in your life that needs urgent attention. The word 'blood' in a dream could mean something you consider permanent. Something written in blood could be passion you have about a project. Blood loss in a dream may mean you are feeling drained. If there is blood spraying everywhere, then you might have a highly charged emotional issue in your life and are feeling like you are literally bursting inside. Dreaming that others are bleeding could be a cry for help.
The taste of blood in this dream is a powerful metaphor representing your feelings of guilt and responsibility.
In this dream, the blood could represent your health. Carrying the blood in the bag might suggest that you are taking chances with your health.
It mean you had a bad dream.
Dreams about blood can have many different meanings depending on other elements in the dream. Similarly, dreaming of one's niece could mean many different things depending on what the niece is doing in the dream. A basic principle in understanding dreams is that the dream is about the dreamer, not about other persons that appear in the dream. So the blood and the niece in this dream reflect something about the dreamer's feelings, memories or experiences.
You will lose something minor/major. (an object, person, friend or etc...)
it means you are having a nightmare and nothing else.
This dream suggests feeling as if someone is trying to cast blame on the dreamer. It reflects the expression of having "blood on one's hands."
you watch too many movies
More information about the dream is necessary for any meaningful interpretation. "Blood" is a powerful symbol that could represent ideas as diverse as the sacrifice of Jesus Christ, childbirth, murder or menstruation. Many girls and young women dream of blood just before their menstrual period begins each month.
A dream about peeing blood could mean that you will be asked to give money to someone. It could also mean nothing, and you just ate a heavy meal before bed causing you to have a strange dream.
A dream is something that deep down you truly want to happen.
The dream provides a picture of your emotional pain. There are times when emotional pain can be so real that it seems it should be visible in some way. So in this dream, your subconscious mind provides an image of the bleeding that would accompany a physical wound, confirming your sense of being wounded.