The faint feeling, low blood pressure, is most likely due to the blood loss, which reduces the number of red blood cells, which contain hemaglobin carrying oxygen throughout the body, and the loss of plasma also, but there could be other underlying causes, such as the reduction of RBC, plasma, by the bone marrow not producing enough due to radiation, treatment, and others like pain medication. Normal hemoglobin is between 13-17dl in males, slightly less in women, so he can still be low, but high enough not to need more transfusions, and each place is different, but should be under 10, and my place was even less with being under 7. RBC continuously die off, and are continuously replaced by the bone marrow, and have a cell cycle of 120 days. I have chronic anemia, and had a number of transfusions, and receive procrit or epogen shots to help the bind martow make RBC, but during treatment, with active cancer, it's not good to have these injections, and have minimal transfusions until the hemoglobin gets really low or in distress, even if it's not extermly los, since the first can cause an increae in tumor size, speed up cancers, and 2nd may increase recurrences, and have other risks, but it does improve QOL. Transfusionx last longer, and act in a few hours, as opposed to the procrit/epogen injections, which take several weeks to be effective with weekly shots. When the hemoglobin is low, you do not want to do anything, even eating, thinking, talking, standing is an effort, causes shortness of breath, dizziness, lack of energy, and I know how this feels.

Good luck with relaying information to his doctors.