As a friend always says - take the head and the body will follow. It is indeed a mind thing. I had a girl once who had an incredible tolerance to pain. Solid stroke just made her wet. But if she accidentally stubbed her toe, she'd be in pain from the tears (and you can only guess at the agony she went through when she had her appendix removed). As ID said, it's all in the manner in which the pain is administered - and the amount of pleasure that is induced at the same time - and that cross-over, from pain to pleasure is very much mental/emotional in nature.