I experience an occasional sudden onset of feeling like I'm going to passout but without symptoms of the room spining. When I realize what is happening I take deep breaths and the feeling passes shortly thereafter. I had my carotic artery tested to make sure there is adequate blood flow to the brain and the results were normal. I do have a small blockage in my aorta but several doctors have said that it is nothing to worry about. What could be causing this feeling without actually fainting?