But just as we're falling short on sleep, Americans are getting less mental downtime than ever. In a survey by the Bureau of Labor Statistics, 83 percent of respondents said they spent no time during the day relaxing or thinking. "People treat themselves like machines," says Matthew Edlund, M.D., the author of The Power of Rest: Why Sleep Alone Is Not Enough. "They consistently overschedule, overwork, and overdo."

This is especially true for active women, who tend to go just as hard in the rest of their lives as they do in their workouts because they're motivated and driven, says Danielle Shelov, Ph.D., a psychologist in New York City. "They think the best way to succeed is by doing as many productive things as possible," she says.

That kind of attitude can rebound on you, though. Consider the zombie-like feeling you have after a marathon meeting at work, a crazy-busy day running errands and doing chores, or a weekend filled with too many social gatherings and obligations. You can barely think straight, you end up accomplishing less than you had planned, and you become forgetful and make mistakes. A full-throttle lifestyle can chisel away at productivity, creativity, and happiness, says Stew Friedman, Ph.D., the director of the Wharton Work/Life Integration Project at the University of Pennsylvania and the author of Leading the LifeYou Want. "The mind needs rest," he says. "Research shows that after you take a mental time-out, you are better at creative thinking and coming up with solutions and new ideas, and you feel more content." (Here's why burnout should be taken seriously.)

Mental Muscle

Your brain is actually designed to have regular rest periods. Overall, it has two main modes of processing. One is action-oriented and lets you concentrate on tasks, solve problems, and process incoming data—this is what you use when you're working, watching TV, scrolling through Instagram, or otherwise managing and making sense of information. The second is called the default mode network (DMN), and it switches on whenever your mind takes a break to wander inward. If you've ever read a few pages of a book and then realized you haven't absorbed anything because you were thinking about something totally unrelated, like the best place to go for tacos or what to wear tomorrow, that was your DMN taking over. 

The DMN can switch on and off in the blink of an eye research shows. But you can also be in it for hours, during, say, a quiet walk in the woods. Either way, spending time in your DMN every day is critical: "It creates rejuvenation in the brain, when you can chew on or consolidate information and make meaning out of what's going on in your life," says Mary Helen Immordino-Yang, Ed.D., an associate professor of education, psychology, and neuroscience at the University of Southern California's Brain and Creativity Institute. "It helps you make sense of who you are what actions to do next, and what things mean, and it's linked to well-being, intelligence, and creativity."

The DMN gives your mind a chance to reflect and sort things out. It helps you expand on and solidify lessons you've learned, think about and plan for the future, and work out problems. Anytime you get stuck on something and give up on it only to be struck with an aha moment later on, you may have your DMN to thank, says Jonathan Schooler, Ph.D., a professor of psychological and brain sciences and the director of the Center for Mindfulness and Human Potential at the University of California, Santa Barbara. In a study on writers and physicists, Schooler and his team found that 30 percent of the group's creative ideas originated while they were thinking about or doing something unrelated to their jobs.

In addition, the DMN also plays a key role in forming memories. In fact, your brain may be busier forming memories in the quiet time right before you fall asleep (a prime DMN period) than when you're actually sleeping, a study from the University of Bonn in Germany suggests.

Get in the Zone

It's important to give your brain a break numerous times throughout the day, experts say. While there's no hard-and-fast prescription, Friedman suggests aiming for a rest period about every 90 minutes or whenever you start to feel drained, are unable to concentrate, or are stuck on a problem.

No matter how busy you get, don't sacrifice activities that really revitalize you, like a quiet bike ride in the morning, a lunch break away from your desk, or a relaxing evening at home. And don't skip vacations or days off. "The key is to stop thinking that downtime is a luxury that's taking away from your productivity," Immordino-Yang says. In fact, just the opposite is true. "When you invest in downtime to consolidate information and construct meaning out of your life, you charge back into your day-to-day rejuvenated and more strategic about what you want to accomplish."

Here are some other proven ways to get the mental refresh you need every day:

Take action. Washing dishes, gardening, going for a walk, painting a room—these types of activities are fertile ground for your DMN, Schooler says. "people have a hard time daydreaming when they're doing absolutely nothing," he says. "They tend to feel guilty or bored. Nondemanding tasks give you a greater mental refresh because you're not so restless." Next time you're folding laundry, let your mind wander.

Ignore your phone. Like most of us, you probably pull out your phone whenever you're bored, but that habit is robbing you of precious mental downtime. Take a screen break. When you're running errands, stash your phone away (so that you'll have it if you really need it), then ignore it for as long as you can. Notice how it feels to not be distracted and the way you can daydream when you're doing things like waiting line. Friedman, who asks his students to try this as an experiment, says people inevitably feel anxious at first. "But after a little while, they start to take deeper, more relaxing breaths and begin to observe the world around them," he says. "Many realize how much they use their phones as a crutch whenever they're nervous or bored." What's more, allowing your brain to drift at times like this may actually help you stay more focused and present when you need to be, such as during an endless but important meeting at work, Schooler says.

Be a little less connected. Facebook, Instagram, Twitter, and Snapchat are like chocolate: Some is good for you, but too much can be trouble. "Social media is the biggest killer of downtime, period," Shelov says. "Plus, it can work against you because you see only the perfection in people's lives. That makes you anxious." Even more stressful are all those upsetting news stories in your Facebook feed. Track your social media usage for a few days to see exactly how much time you're spending on it and how it makes you feel. If necessary, set limits for yourself—no more than 45 minutes a day, for instance—or cull your friends list, saving just those people you truly enjoy keeping up with. (Did you know that Facebook & Twitter rolled out new features to protect your mental health?)

Choose nature over concrete. Letting your mind wander while you're strolling through a park is more restorative than when you're walking down a street, according to research from the University of Michigan. Why? Urban and suburban environments assault you with distractions—honking horns, cars, and people. But a green space has soothing sounds, such as birds chirping and trees rustling in the wind, that you can choose to pay attention to or not, giving your brain more freedom to roam where it wants to go. (BTW, there are plenty of science-backed ways getting in touch with nature boosts your health.)

Peace out. The mindfulness you get through meditation delivers important restorative benefits to your brain, studies show. But that doesn't mean you need to carve out a half hour to sit in a corner and chant. "There are plenty of rest and relaxation techniques that you can do in under a minute," Dr. Edlund says. For example, focus on the tiny muscles in different areas of your body for 10 to 15 seconds each, he says. Or every time you take a drink of water, think about how it tastes and feels. Doing this is equivalent to giving your mind a mini recess, Friedman says.

Follow your bliss. DMN isn't the only kind of mental break you benefit from. Doing things you love, even if they require some focus— reading, playing tennis or piano, going to a concert with friends—can also be rejuvenating, says Pamela Rutledge, Ph.D., the director of the Media Psychology Research Center in California. "Think about which activities fulfill and energize you," she says. "Build in time for that enjoyment and to experience the positive emotions that come from them." (Use that list of things you love to cut out all the stuff you hate—and here's why you should stop doing things you hate once and for all.)