Randy, I wouldn’t sweat a thing. Take Sunday off and then resume normal training, which is an easy day Monday. You don’t need to catch-up at this point. When I’ve had a bad day, or am excessively tired, I think nothing of taking some rest. Heck, I had three days last week of 0, 6, and 3.8. At some point the body needs to absorb the training.
Training is like this, try and hit your key workouts (2-3 a week usually if counting the long run) and run the rest at a comfortable pace. I can tell you from personal experience that I have off days. This is why I seldom time my intervals anymore. Becoming too focused on split times can wear a person out. You don’t have to prove to yourself every week that your in shape. You are.