I know that some runners (or exercise fanatics of other ventures) hate this word. However, I think it's a vital part of your workout. Your body needs time to recoup and just rest.
I think if God even made a whole day for this specific purpose, we should honor that. I know you aren't all Christians, but resting seems to be a natural thing regardless. Now, I'm not talking about a month of rest after one day of working out. I'm not talking about being a sloth or laziness (although I still really have to fight those deadly sins).
I'm talking about rest. One or two days of rest in your week (more if you've been ill, injured, or given birth). I used to have Sundays as my day of rest - makes sense. However, I've been calibrating lately that Wednesdays are busier, therefore I need the rest on that day. We'll see how it goes.
You also need to rest while working out. What? I know that doesn't really make sense but look up HIIT training and I'm sure Google will find someone to explain it better to you. I went through the Insanity program about a month ago - 2 months of physical torture. I loved it! But even they rest in the DVD. That was my favorite part of the DVD; most often in DVD workouts, they don't rest. That's annoying because going non-stop without water for 20-60 minutes without water seems silly to me. I like water. I take my first drink of water within a quarter mile of my runs.
But I'm no stranger to rest.
I rested while I went to the Philippines. I rested after my half marathon and my toe was recovering from metatarsalgia. I rest at least one day a week, always. Sundays are my day of rest. I rest during nap times (sometimes too often and too much). Sometimes I even take walking rests during my runs. I really like to rest (see? that's laziness for me).
It's just healthy to take a rest sometimes. A body rest, a mind rest. It's ok to push yourself to the limit most days (I have a friend, Shelly, who runs every day even - and that works for her!), but I am a firm believer in rest. A little R&R.