Anemia means you have too little red blood cells in your blood. The red blood cells are needed for the body's various organs to get enough oxygen. Anemia can cause you to become tired, dizzy and have a headache. Often it is possible to recover the amount of red blood cells with the help of drugs.
Here you can read more about diseases of the blood, for example about different types of anemia and hemorrhage.
Anemia due to too little iron is common and can make you feel tired and powerless. The most common cause of anemia is that you have lost blood. For example, it can be during menstruation or if you have a stomach or intestinal disease that causes bleeding. It may also be because you cannot absorb iron from the food.
Vitamin B12 is needed for the body to form red blood cells. If you have too little B12 you may have anemia. B12 is not produced in the body but you get it through the food. B12 is found in food from the animal kingdom, mainly in meat and dairy products.
Hemorrhagic disease is really a group of diseases. Hemorrhage means that you start bleeding more easily and that you can bleed longer than a person who does not have hemorrhagic disease. This is because the blood lacks one or more substances needed for it to live. Hemorrhagic disease is usually a hereditary disease.
Polycythemia means that you have too many red blood cells in your blood. It makes the blood flow thick. Polycythemia can be a disease but it can also be a consequence of other diseases. The treatment you receive depends on what form of polycythemia you have.