Has anyone seen a dog "sleep wagging"?

I saw an amazing thing: K9 Scout wagged her tail while in a deep sleep.  Her tail was wagging in a happy, soft, playful manner.  I have seen sleeping dogs shake, quiver, and "run," but never wag their tail. Please share any similar experiences or insight.  Here is one theory, Scout's "sleep wagging" occurred after flying in a small 4-seater plane for the first time.  Perhaps Scout found her bliss and was reliving her flying experience.

Maybe Scout was dreaming about being a pilot.