A China Southern Airlines McDonnell Douglas MD-90-30, flight CZ612 from Osaka (Japan) to Shenyang (China), was enroute over the Japanese Sea about 25 minutes into the flight, when a Japanese passenger walked to the bathroom and collapsed onto the floor. Cabin crew immediately attended the passenger, who was pale and not responsive, figured the passenger had suffered a circulatory failure or diabetic shock and managed to stabilize the passenger with sugar and shock treatment, so that he got responsive again and gradually improved to recovery. The flight crew in the meantime requested priority and accelerated the 2.5 hours flight to Shenyang, where the passenger - after expressing his gratitude to the cabin crew - was handed over to a waiting ambulance.