Most Americans will leave about nine days of vacation time on the table this year, according to a new survey by Hotwire. Why are we working so hard?

It’s partly out of fear. Americans are afraid their bosses will think they’re lazy or that their job could get eliminated while they’re away. But not taking vacation matters. John De Graaf, who made a documentary about overworked Americans called Running Out of Time, has found there is a high cost to not taking vacation.

“Women who don’t take regular vacations are anywhere from two to eight times more likely to suffer from depression, and have a 50 percent higher chance of heart disease,” he says.

For men, the risk of death from a heart attack goes up a third.

“We are just like cellphones and iPads — we have to be recharged on a regular basis, says Joe Robinson, a consultant with Optimal Performance Strategies. He says all this work isn’t necessarily making us more productive. And it comes with a huge price tag: “$344 billion a year.”

That’s the amount American businesses spend on stress-related health care costs, according to a study by Middle Tennessee State University.

We want to hear from you: How many vacation days do you get each year and how many do you use? Tell us on Facebook or in a comment below.