'slipped disk' is most probably a disk herniation (rupture). My experience is that the cause is that your spine is not supported sufficiently. I had a couple of episodes of this when I was younger. I did some research and read a book on the subject (the internet was in it's infancy). The book recommended strengthening your abdominal muscles so they support your spine. It worked for me, very occasionally I have a back ache but nothing that stays with me.

I doubt that any manipulation/massage can have any long term affect and may cause more harm than good.