(Fortune) -- Dear Annie: Until last year, my family and I always managed to get away for two weeks of rest and recreation every summer. For reasons you can guess, I took no time off last year and now, at about the time I'd normally be reserving a cabin by a lake for ten days or so in August, I'm really hesitating to make the call.
For one thing, my boss works all the hours God sends, and likes to brag about how he "hasn't taken a vacation since last century" (meaning, I think, 1999). Another thing is, everybody here is working flat-out and I have one colleague in particular who looks horror-stricken if I mention the possibility of taking a break. Should I just take a vacation anyway? It's part of my compensation, isn't it? --Tired
Dear Tired: It is indeed. I never cease to be amazed by people who wouldn't dream of giving back part of their paycheck, yet who don't take the time off to which they are entitled. A survey by Expedia.com found that only 10% of employees who were allowed a two-week vacation actually took it in 2009, down from 14% in 2008. In all, the poll says, 34% of U.S. workers don't use all their allotted vacation time, giving up an average of three days off per year.
That amounts to "a $20 billion giveaway to America's employers." says Lois Frankel, Ph.D., president of Pasadena-based Corporate Coaching International, whose clients include heavy hitters like Lockheed Martin (LMT, Fortune 500), Warner Brothers, Walt Disney (DIS, Fortune 500), and TRW (TRW, Fortune 500).
"It's not just money you're losing" by skipping vacations, Frankel adds. "It may be your health as well." She points to studies showing that women who take two or more vacations a year cut their heart attack risk in half, compared to women who take no time off; and men who take frequent breaks are 32% less likely to die of heart disease.
Moreover, although some folks think ceaseless toil will help them prove they're indispensable, Frankel says it doesn't work that way: "Unused vacation time never makes or breaks a career."
Still, in these insecure times, a little extra attention to detail may be well worth the effort. She offers these 5 suggestions for making sure your job will be waiting for you when you get back:
1. Schedule your vacation well in advance. Giving everyone plenty of notice that you'll be away is important for planning purposes, of course, but it also can't hurt to remind people as your departure date approaches. "Don't expect your boss to remember," Frankel says.
2. Don't plan a vacation for "crunch" times or when a big project is looming. Enough said.
3. Leave nothing dangling. Especially now, when everyone is working flat-out, be careful to wrap up any important business you've got cooking before you take off -- or, at the very least, enlist someone to act as your point person while you're gone.
4. Consider taking long weekends instead of a two-week vacation, if that seems to make more sense. Enjoying several 3- or 4-day weekends throughout the year has been shown to create the same energizing, stress-reducing effects as a single long break, and may be more practical as well -- at least for now.
5. Unplug while you're away. Try to turn off the cell phone, BlackBerry, and laptop while you're lounging lakeside -- or better yet, don't even pack them. Easier said than done, since a whopping 79% of people in a recent poll by Osterman Research said they brought a work-related device with them on vacation.
But "vacations play a big role in superior job performance," says Frankel. "That only happens when you return relaxed and refreshed."
Let's suppose you've done everything right and your "horror-stricken" colleague still objects to your temporary absence. What should you do? "Stand your ground," says Joseph Grenny. co-author of a New York Times bestseller called Crucial Conversations: Tools for Talking When Stakes Are High (McGraw-Hill, $16.95).
"You have to maintain boundaries," says Grenny, who is also a co-founder of Vital Smarts, a Provo, Utah, consulting firm that does training and organizational development work with big employers like IBM (IBM, Fortune 500), Texas Instruments (TXN, Fortune 500), and Sprint (FON). "If your colleague is overworked, that is an issue he or she needs to deal with as an entirely separate matter from whether you take a vacation or not. Have an explicit conversation about it. Be polite and respectful, but don't let this person guilt you into giving up the time off that you've earned."
As for your workaholic boss, he's doing the company no favor in the long run, says Grenny: "We worked with one organization where turnover among skilled employees was very high, and it was terribly costly. When we looked into it, we found that senior management was working 50- and 60-hour weeks for years on end without ever taking time off. So the people under them did the same -- and eventually burned out and quit."
To avert this problem, "bosses have to set the right example," he says. "If you're a manager, it isn't enough just to tell people, 'Take your vacation!' They won't believe you mean it, unless you also take yours."
Talkback: Have you cut back on time off, or given it up entirely, the past couple of years? Has it made you more or less productive? Are you skipping your vacation this year? Tell us on Facebook, below.