Since the dizziness has always been seasonal. At a time one tends to close down the house for warmth. Do you use an open fire? Or is there a possibility that the heating is creating fumes? that may be the reason for your dizziness?
The problem may be a lack of fresh air since doors and windows are often firmly shut and since qigong is an exercise that focuses on the breathing the lack of ventilation may become even more apparent. I suggest trying to do your qigong exercise further back from the heat source or perhaps the room with more ventilation.
Alex
