Fatigue lowers all of your stats. Lowered endurance = more pleasure damage taken. And the combat system in this game is a balancing act, if your stats are near theirs you take a reasonable amount of damage, or next to none. But as soon as your stats get lower than theirs you take more and more damage.
So the combination of stronger enemies on floor 4 + fatigue from Karryn makes her take a shit load of damage. Even move if you have all the edicts to make enemies stronger. I have all the +enemy stat edicts and I fought the Yeti boss without really leveling up much from the previous level cap and this was the result at the end of the battle.
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She would go into a orgasm chain from the slightest touch, a spank could cause her to orgasm from 0. And my base endurance is 120.
Moral of the story, be careful of the +enemy stat edicts.