An intern at my firm once said, "There's never a good time to take a vacation, so you might as well take one whenever you can." That's good advice. There will almost always be a deadline, a problem, a crisis looming that will deep-six even the best-laid plans. Follow those plans anyway. Leave the office. Don't cancel the trip--go. If you can't afford to leave town, tell everyone you're going camping in a remote area. Then don't check your phone or email. I've actually not checked my phone or email for a week, and it was immensely restorative. My husband and I went to Yellowstone last year for an early birthday trip (the first week of September instead of the last week), and we watched no TV and checked no email. It was some of the best sleep and rest I'd ever gotten in my life, and we're looking forward to unplugging on this trip as well.
I encourage all of you to take your vacation time, and really take it--unplug and don't be available. Everyone will miss you and be glad to have you back, but they won't die while you're gone. The work will be there when you get back.