You're earned it. You need it. Your mind and body will benefit mightily from down time — nowhere-to-go, nothing-to-do time to relax, refresh, reconnect with nature, read a good book, play with your kids. All these activities and a zillion more will alleviate your stress and increase your joy.

It rocks my hammock when I read that most Americans don't take all their vacation time. The average U.S. worker got a measly 18 vacation days last year — lower than France, Germany, England and other industrialized nations — and only used 14 of them, according to a 2010 survey by Expedia.com.

In fact, only 38 percent of Americans surveyed say they take all their vacation days. This hurts my head. Some reasons? Their bosses aren't supportive. (Try a bar of Scharffenberger 82 percent cacao extra dark chocolate.) They don't have extra money to pay for vacations. (Who says vacations have to cost money?) They're afraid that if they can go away, so can their job. (Letting go of fear is a liberating practice.) One more depressing survey finding: 72 percent of Americans who do take time off call in to work — some of them every day. Oh, dear.

There's a cute name for this problem: Vacation Deficit Disorder. If you've got it, only you can find the cure. It lies within, where that healthiest part of you yearns to play tennis, or hike in the woods, or dream on a beach. Living a healthier, happier lifestyle isn't just about more time at the gym, or less time with taco chips. It's about finding balance in your life. All work and no play is a prescription for disaster. Summer vacation isn't just for kids. You're earned it. You need it. Take it!

And when you do, here's how to avoid gaining those 5 to 10 pounds that can creep up on you when your fun level rises and your guard goes down:

CAR TRIPS. The desire to snack goes from zero to 60 on a road trip. If you rely on the toxic junk for sale at most gas stations, you're in trouble (though I admit the choices are so much better than they used to be).

Smart travelers pack a cooler of healthy nosh: fresh fruit, raw veggies, seeds and nuts, air-popped popcorn, etc. Also, schedule exercise and stretching breaks into your traveling day. Just three 10-minute walks can add the recommended 30 minutes of daily activity and help you avoid the lower-back pain that comes from too much time at the wheel.

CRUISING. Cruise ships are floating fat factories. My spirits sunk when I read that the average person gains 5 to 7 pounds on a one-week cruise. So practice moderation, please, and take full advantage of exercise facilities onboard. Walk the deck, do laps in the pool, dance 'til dawn. At the eat-till-you-explode buffets, limit yourself to one trip. Ok, two. Load half the plate with veggies. Avoid cream sauces, fried foods, the cornucopia of cupcakes. If you do splurge, eat lighter for the rest of the day.

HOTELS. Always pick a hotel that has a good fitness center. A vacation day that starts or ends with a vigorous workout gives you the energy to have your best time. Many hotels offer maps with nearby walking or running routes, so explore the possibilities with the concierge when you arrive. I like to find a good yoga class in any city I'm visiting. It's a great way to meet the locals and get their recommendations about interesting restaurants, live music, tattoo artists, etc.

PLAN AN ACTIVE VACATION. The choices are endless: camping, kayaking, hiking, horseback riding — you pick. My favorite is a bike trip: Cycle all day at whatever pace you like, and you won't have to count calories at night. Plus, it's a fabulous way to tour. The sights, the sounds, the smells. A bike transports you to a new way of seeing the world so you can return to everyday life, refreshed and renewed. That's what vacation time is all about.

ENERGY EXPRESS-O! SLEEP ON THIS

"A vacation is having nothing to do and all day to do it in." — Robert Orben

Marilynn Preston — fitness expert, personal trainer and speaker on healthy lifestyle issues — is the creator of Energy Express, the longest-running syndicated fitness column in the country.