Sometimes the most hardcore thing you can do...

...is to take a day off.
I didn't run today. I'm finally listening to my body, which gave me a bit of a cold a few days ago. But I just had to run those 30k this weekend to hit my weekly kilometrage--at least I didn't do the long run on trails at an ungodly hour of the morning with wind chills probably below -15C.
Coincidentally, there was a blog post on the NYTimes Well, which doesn't say anything you shouldn't already know, but it was nice to get a reminder to take things easy:

Experienced athletes know that the only way to improve is to push yourself. Lift weights that are heavier than those you’ve tried before. Run or cycle at a fast pace on some days, but focus on increasing your distance on others. Work out enough that you may not fully recover between sessions.
You should feel tired, said John Raglin, a sports psychologist at Indiana University. But if you do too much with too little rest, your performance gets worse, not better.
http://well.blogs.nytimes.com/2012/01/16/personal-best-workouts-have-their-limits-recognized-or-not/ 

I used to think that I was a two, at best three day a week runner--that anything more would just lead to injuries. That was because I went way too hard on my runs--pushing myself to the max every time. The most important run for me to learn was the recovery run--learning to go easy and short. Once I discovered that the trick of training is to go slower so you can go longer and more frequently, I was able to six days a week. I guess last week was too many tough days. Way too many! A 10k race, a 26km fasted long run (slow, but still...), a hard tempo workout, striders on an easy day (which I'm not used to), and a decent speed workout too. No wonder I got the sniffles.