Pack Failure
The 777 used to do this regularly. Apparently there was an Auto Slat command being fed into the Air Supply Cabin Pressure Controller and it shut of the packs in a way to preserve engine power as the A/C thought something really nasty was about to happen. Boeing sent out an alert which basically said not to worry if this happens for up to 60 (or 90?) seconds; this is perfectly normal and a known glitch....