I talked with my Doctor this morning, he happens to be a good friend of mine, and asked him what he thought. He says that most likely what is happening is that the intensity of the exercise is releasing sinus fluid. The key is the color of the fluid. If it is frothy, thick, or worse yet green, then I would have a problem. Also, if there were shortness of breath that continued through out the day then that would indicate a problem. So I think it is likely that it is just a sinus issue that becomes apparent after the intense workout. No worries. Thanks!