The song comes from the Anglo-Saxon Rune Poem and is in two languages. The first is a modern German translation of the second, which is in Anglo-Saxon.

Fylgija is a Norse name for the 'spirit'/fetch that can shape-shift into an animal while a sorcerer is asleep 'dreaming'. For an excellent reference on this, check out Claude Lecouteux's book 'Witches, Werewolves and Fairies: Shapeshifters and Astral Doubles in the Middle Ages'.