Daisy,
I found that when you play, you pay. It is called overdoing it. You have to know when to stop what you are doing, rest or nap, then continue on.

If you push past the fatigue point, like we all do at times, the next day or two you will have to rest up. Our body doesn't like to be pushed too hard. It is a signal from our brain to take it easy and rest, or pay the piper.

As Kicker said, there is spoon story, that explains it very well. Maybe she still has a copy of it to show you.