Last week, on my last full day before taking off on vacation, I had a busy day, as usual. I wrapped up a story for FORTUNE, hosted a webinar for GreenBiz.com, wrote a blogpost, pushed through my email, which now arrives at a rate of 100-200 a day, and ran a couple of errands.

In between, by coincidence -- or perhaps not -- I stumbled across a couple of NPR interviews. Diane Rehm talked with Dr. Herbert Benson of Harvard Medical School about his new book, Relaxation Revolution, and Terry Gross of Fresh Air interviewed Matt Richtel of The New York Times about his excellent series of stories, called Your Brain on Computers, which explores how digital media is changing our lives, our culture and, yes, our brains. The interviews were so compelling, and so timely, that I listened to both programs, in full, this morning. (They're available on iTunes.)

Both were, in a way, about the same thing: how stressing the brain affects health. And while many things are more stressful than being "always on," facing tight deadlines and being nagged by that feeling that you haven't checked your email, oh, in the last 45 minutes, most of us will never go to war or perform surgery, so these are the of stresses that touch us every day. They can literally be deadly -- Richtel won a Pulitzer Prize this year for his terrific series of stories, Driven to Distraction, about the risks of talking and texting behind the wheel. (One of my very top pet peeves is people who talk on the phone while driving.)

Richtel had some fascinating things to say about people (and you know who you are) who can't sit with their own thoughts for even a few minutes while standing on line at the supermarket or coffee shop, and have to pull out their smart phone to check email or play a game. Constantly being barraged by information, it turns out, may make it more difficult for us to absorb and remember things; the brain, it seems, may need downtime to recharge itself, even if it's only a few minutes a day. He also said (and this makes total sense to me) that being connected all the time gets in the way of daydreaming and "boredom," where many of our most creative thoughts occur. (I try to occasionally drive my car without the radio on, and my mind sometimes takes me to interesting place.)

Richtel also talked about why we need vacations, and in particular about an excellent story he wrote about a trip he took with a group of brain scientists who went off the grid for a few days. Scientists, it turns out, are starting to study what happens when we step away from our devices and rest our brains.

Benson, who is in his mid-70s, is a pioneer of mind-body research. His book, The Relaxation Response, was a best-seller in the 1970s, and he argues that all of us would enjoy better health if we could find 10-20 minutes a day of quiet time -- meditation, yoga, prayer. I've never been able to maintain a meditation practice (running's the closest thing) but I have no doubt that this is true. Many successful and busy business people, notably Ricardo Levy, who is very wise on this topic, carve out quiet time every day.

None of this will come as news to people steeped in Buddhism, Christianity, Judaism and, probably, a bunch of other religions with which I am less familiar. Buddhists understand the value of quieting the mind. Practicing Christians and Jews observe a day of rest. There are lots of good books about this but let me plug Sabbath Sense: A Spiritual Antidote for the Overworked by my friend Donna Schaper, a United Church of Christ minister.

What does all this have to do with sustainability? Well, at the most superficial level, we all need rest to keep doing what we are doing. Being "always" on is ultimately unsustainable. More that that, the idea of resting and restoring (the earth, your workforce) are part of a sustainable business practice.

So I headed off on vacation with a clean conscience and the hope that I could mostly stay off email. (AT&T's absurdly high international data rates will help; my wife and I are going to Italy.) I'll be back after Labor Day -- yet another reminder that most of us need to build more down time into our lives.

_{Photo licensed by artM.}