If you are feeling sluggish, sore, or beat, it is a good sign that you could use a day or two off. Many think that if they miss a workout every now and again, their progress will slow down or stop. This is not the case; a day off may actually help speed up recovery!!!
When we are working out we are literally tearing our muscles apart. Afterwards, our body repairs them and we end up stronger and faster. We don't getting stronger by lifting weights or get faster by running/sprinting, but rather by resting!
If our bodies can't recover in the time between workouts, we are actually limiting the progress we can make. So how do you know if you need a day or two off (or three)? Well,
typically you need some time off if....
1) You don't have enough energy to make it through the workout 2) You aren't able to perform at the same level as before 3) You have aches and pains outside of muscle soreness
The best thing to do on your day off is simply rest. Get some extra z's, eat some solid, healthy meals, and relax. Watch a comedy, read a book, whatever you need to do. If you get antsy and need to move around, do some sort of low intensity exercising like walking.