Clearing your head is important. Unfortunately, many people seem to forget that it is necessary. "The physiological effects of tiredness are well-known. You can turn a smart person into an idiot just by overworking him"[1].

Also: Getting out the door is good: Five minutes of "green exercise" turns out to be good for your mental health[2].

[1] http://money.cnn.com/2006/03/16/news/ecanomy/annie/fortune_a...

[2] http://www.acs.org/content/acs/en/pressroom/newsreleases/201...