I was on QF568 from Perth to Sydney when our plane suddenly experienced a serious cabin depressurisation issue affecting the whole planes cabin pressure. 2-hours in flight, the pilot announced over the PA “emergency decent, emergency decent”! The aircraft jerked violently and rapidly descended, as oxygen masks fell from the ceiling. Three people fainted as the aircraft was suddenly descending! We got diverted to Sydney and landed safely. That was the most scariest experience of my life!