So I've been listening to the audio books of the Lightbringer series by Brent Weeks and there was a passing mention of something that should be horrifying to normal people. In the books, one of the characters is a slave and is threatened with being sent away to a salt mine(I think) where she would be used as a 'bed slave'. Basically, a whore, but not just a whore. A whore for the most vicious people, since the mine is mined by vicious people. The whores don't live long, because they're constantly in use by the miners, used '50 times a day' as the book describes.

So the question is this: what kills them? They're slaves being raped to death, but what causes the death? Surely there are 'accidents' or merely an especially vicious person getting carried away, but assuming more 'natural' causes, what would cause a person to die from over sex? Assuming proper nutrition(a specific case of a slave surviving for I think something like 5 months is mentioned), I would imagine it would have something to do with madness and emotional death followed by physical death, but how would such a thing manifest? Heart failure?