It's amazing how your body lets you know what it wants/what you need. Today was the first day in a long time that I craved a Gatorade. This happened right after I got off the bike (on a stationary trainer in my living room, don't worry). Mind you, I had been taking water on the bike.
This evening, I got hungry again, after eating my regular meals. My body needs more food than I have been giving it in the past month. It lets me know. I had a second dinner and ended up taking a protein shake after my second bike workout.
It's amazing when you crave salt or water or sweets that those things are probably what you need. I've always thought of "listening to your body" as stopping/cutting back on workouts when you hurt. I guess it's just as valid to listen to the body's demands for sleep and nutrition. MAYBE, you could even listen to your body's demand to go farther (although, most of the athletes I know must push their body with their mind since the body wasn't designed to suffer endless workouts voluntarily).