The phase where a guy has the need to sleep all day for several days. This could be due to a breakup, they constantly have nothing to do, or they're just really lazy.
Similar to Bears and other animals where they sleep for the winter.
Bob: Have you seen Dave lately? I haven't seen him in a bout a week!
John: Yeah, he's in his Guybernation phase.
Deciding to take a break from guys for an extended period of time.
Elisa: I'm so tired of men... I think I'm going to go into guybernation for a while.