@Fragmentbe I'm sensing you don't have much experience with strenuous exercise.
When you overexert yourself compared to normal in exercise, you feel extremely sore the next day, but not really all that much the day of (unless you actually strain something, but you wouldn't get that just from too much yuri sex... although I can tell you from experience that having sex too intensely for too long has essentially the same effect on your body as any typical extended period of strenuous exercise, so having a very long session of sex when you don't normally go further than an occasional quick, single session is more or less the same as going jogging for 8 miles when you normally just walk for 2).
In other words, rather than sleeping it off, they would've woken up far more sore than they were before they fell asleep.