Training is pleasant, and makes you feel energetic. However, when looking for performance, training has to be managed, and focused.
To maximize your effort, your muscles have to be well rested. Not resting properly hinders your fitness, and slows you down. It also significantly increases the risk of injuries
Easy days and rest days must be respected more than the actual training. They are the gages of your performance.
It's natural for most to assume that because exercise is critical to improved fitness it's the only thing that matters.
When to run hard, when to race, when to go easy, when to rest, are very important factors that work hand in hand. There has to be a balance within your training schedule to get the most benefit.
If you don’t feel ready, cut your run by half, or turn it into a recovery run. Better yet, take the day off. You will definitely enjoy your next workout.