I agree with drake7. I think that the key will be in asking for what you want. You might even include that as part of the play. As a scene, have your Master torture exactly what limits you'd like broken and a few different ways to do it.

But please do be as safe as you may. Perhaps set up rules of some sort, make sure you've a day or two off from work afterwards to pull yourself back together... and aftercare! Beg your Master to stay and comfort you afterwards or have someone in the know on hand to make sure you have food, tissues, and any medical care needed after it all goes down.