Does CX not have an approved fatigue policy? Here in the States, if you are fatigued you are required to call in fatigued and the only question the airline can legally ask you is when you will be fit for duty. Fill out a fatigue report to make sure you get paid, end of conversation. I have done it on a few occasions. It's really the only way to get rid of onerous pairings. Surprised a high caliber outfit like CX doesn't have something on the books and is not required by regulating authority to implement a fatigue system..