Most coaches will plan easy days and rest days in your training plan. In many respects, these are more important than the hard workout days, so you need to go along with that plan.
Why? Because the way that you build muscle strength is to stress your muscles, then let them rebuild/regenerate. Every time you stress your muscles, you break them down and they need to "heal." As young people, you need less time for this process than I do, but you still need it.
When your coach has you run a hard workout, like, say, 5x1000m, you will probably be doing an easy run the next day. Do it. Don't go out and try to beat your teammates, racing along at some crazy pace. If your coach says to run at a conversational "jog," it's for good reason. If you don't get the rest that your muscles need to build themselves back up, you will likely get injured.
Sometimes your coach will prescribe an off day. These are important, too, so don't go out and play 3 hours of basketball with your friends. Rest. Do your homework. Go see a movie.
One of the other key functions of an easy day or rest day is that it recharges your brain. It can be mentally taxing to run day after day after day after day.... When you take a day off, you will find that you are more ready to run the next day. You'll feel like you missed running and can't wait to get out there and run, instead of dreading the day's workout.
The only thing to avoid regarding resting is resting too many days in a row. I used to think that it wouldn't really harm you if you took 3 or 4 or 5 days off in a row, but I'm changing my mind on that. There are times when you might get sick and you should take more than a couple days off in a row, so that's OK, but I would recommend at least getting outside and walking for 30 minutes or so. That probably won't hurt your recovery from the illness (unless your doctor says to stay in bed or something), and it may speed things up by getting out and getting some fresh air, getting some blood pumping, etc.
Three-day weekend coming up - you should be running on at least two of those days, but REST, too, if that's on your schedule....