New research says that it takes Americans four days of vacation before they can actually stop thinking about work. A study conducted by OnePoll in conjunction with Apple Vacations looked at the vacationing habits of 2,000 Americans and found that they only spend three full days of a seven day vacation feeling completely relaxed and not worried about work. Other findings include: 79% of Americans struggle to get away for vacation and end up not using all of their vacation days. 37% of Americans end up feeling guilty about leaving unfinished work at the office — and this was the reason they avoided taking vacation. Another 26% said that they worry that taking vacations would prevent them from getting a promotion.