The phrase "fire in the head" is a Celtic metaphor
for divine inspiration
. It ultimately derives from the "Song of Amergin
," but has cognates in the poetry of Taliesin
, whose very name means "Shining Brow."
It also appears in W.B. Yeats' poem "The Song of Wandering Aengus":
I went out to the hazel wood,
Because a fire was in my head.