The “real” pose that’s closest to Serene Possum is Corpse Pose, or Savasana, and here’s a little more about it:

http://yoga.about.com/od/yogaposes/a/savasana.htm

Let the toes fall outward or inward, whichever feels most natural.

Arms are also relaxed, resting on ground, at any angle that allows the muscles to “melt.” Elbows may be bent in the most comfortable position.

Palms up or down, whichever is more relaxing. Hands should curl naturally.

Slow your breathing, and take deep breaths. Head may turn to one side, if that feels easier on the neck. You may close your eyes.

The name of this pose is “Serene Possum”. I typically end my own training sessions with this pose, or even after a hard set. My clients will also usually finish their workouts in this position, uttering the ancient chant/prayer of “thank God the workout is over” or something similar. Interestingly… I don’t think I’ve never had to explicitly teach anyone this pose, so I’m inclined to believe it’s something inherent to our human nature.

Here is a photo and a video for Serene Possum.