What are the actual temperatures? Do you have a thermometer and hygrometer in the cage to monitor it? Just putting a light may not be warming it as much as you think.
Also, please post the answers to the questions in that sticky.
Yes, flipping is a sign of stress in pacs. Either that or a much more severe problem, but most likely stress. Think about it; being on its back is in no way a natural position for a pacman frog. Stress can kill amphibians quickly, so the problems need to be corrected as soon as possible.