New iTunes update deleted all my music?!

I simply opened up my iTunes app this morning, and it updated before opening, and i was very VERY frustrated and angry to find that my entire music library had disappeared. Except for the 20 songs that i actually purchased from the iTunes store. I hate the new update, as it is basically spotify, and it deleted over 600 songs i had downloaded from Incompitech, Youtube.. ect. I am far from furious right now.