Also fade up. to increase or cause to increase gradually, as vision or sound in a film or broadcast
To my thinking, the song means that she experiences something similar to ''dizziness immediately after standing up'' wich can provoke blackening or fading out of vision, (fading out being a slower decreasing of it and then coming to normal). The song has (figuratively) likened it to the passion, the infatuation at its climax. Like someone that lusted for another and is with him now, so all senses fails her, everything is good, she do things without thinking about consequences. It´s a wonderfully horrible change...
It´s not for a reason that infatuation and dizziness are so talked about and likened, in movies, poetry and music.Fading in, fading out
On the edge of paradise
Every inch of your skin is a holy grail I've got to find
Only you can set my heart on fire, on fire
*Cause I'm not thinking straightMy head spinning around I can't see clear no more
What are you waiting for?
*She is dizzy with love
. (figure of speech here)
*A symptom of Dizziness as well, imagine "someone on the edge of a cliff (that she may have changed to "paradise" and have the sensation of head spinning!
In Hitchcock´s (and other movies) fading in was a movie effect, where the scene and the characters "disappeared" (fadded in) marking the transition to a new scene "fad out" (as in pop out, remember that comtemporary word? okay, "out" being "coming out" of sorts... )http://www.alostfilm.com/2012/11/vertigo.html
transitions, fadding-outs at 1' (minutes) 18'' (seconds); 0' (minutes) 18'' (seconds); then at 1' (minutes) 37'' (seconds). Obviously, at that time it was a bit slow, now they make it more abruptly (the effect) sometimes.
Redseahorse answer is a concise and proper translation. I just added my two cents worth, just for information´s sake.
In fact the song has more imagery to it, but let´s leave it at that.