Fall asleep, restoring 197 health on the first round, 394 health on the second, then 788 health on the third.
While Hibernating you cannot swap pets.
Achievement: WoW's 4th Anniversary
Category: Feats of Strength
Pet Battle: [3-6] Darkshore
Vendor: Derrick Brindlebeard
Cost: 40 (unlimited supply)
Vendor: Varlan Highbough
Zone: Molten Front
Cost: 1500 (unlimited supply)
Pet Battle: [6-7] Hillsbrad Foothills
Promotion: World of Warcraft Collector's Edition
Quest: Beasts of Fable 
Drop: Fabled Pandaren Pet Supplies
Approximate Drop Rate: unknown