The first question is whether it is a genetic situation or an exception occurring while you do heavy lifting. If you are the former, I assume that you may just suffer lack of oxygen. As we all know, when we try to stand up or squat quickly lifting a heavy object, our blood will rush out of your head in order to guarantee a rich blood supply in the arms and legs. As a result, we may feel dizzy attributed to the insufficient blood in the head. Further, a sudden rise of blood pressure has health hazards. In addition, you can try to take a deep breath before you are upright and exhale hardly when you are done. Rest a while after doing a set. So, your concentration on breathing can really help. If you are the latter, you may suffer anemia, which can be improved by balancing your diet, I mean, you need take in more food with an high iron content.