Good article. 

The Arctic Ground Squirrel (AGS). Hibernation isn't actually sleep. It is a state of extreme metabolic suppression during periods when obtaining resources may take more energy than the resources provide. They spend up to nine-months lowering & raising metabolism & body temperature somewhat regularly (based on burrow temperature), with torpor (low) bouts lasting 18-21 days, & arousal (high) bouts lasting about 12-18 hours. 

In torpor, body temp can be as low as -2.9C (below freezing), they show almost no brain activity, heart beats ≈4X/min., respiration is sporadic & fairly rhythmless. Basically they are just keeping the fires burning as low as possible. When they warm (arouse), they don't usually get up & move around, they just warm, heart rate, respiration, metabolism, temp, & brain waves increase. One explanation for this might be, that they need to dream - to reinforce neural connections - or they will "forget" they are a squirrel. 

Or so I heard on the street :-)