I too would get a note from your physician. I would be diligent about being a top notch employee, since accomodations are being made for you. IN a pinch, I would offer to do what you feel like you might be able to handle at home. However, you are limited by your illness and should not hesitate to speak up. If you are a good employee, are willing to pitch in at home in an emergency and have documentation of your illness and need to not work OT, and they do not cooperate, then you might have to consider looking for another job. If they are abusive, I would consider legal counsel.