perhaps that is a sign that you are waking up and your dream world is de-materializing and is becoming unstable? Does this all happen quickly or slowly? Try sitting down and rub your hands against the ground or against eachother and emphasize on the feeling or concentrate on a detail in your dream. That is of course if your dream fades quickly.

or if it happens slowly then i suggest going into or creating another dream world by either spinning or using other means via mirrors or portals.