You can lose points below 0, however, the house will only loan you 10 points. So, if you dip below -10, the game is over.
You can, however, use one of your optional toys, like a butt plug, nipple clamps, gag, etc. and the house will forgive your debt and you can restart the game at 0 points. However, you must then leave that toy on for the remainder of the game.