The only thing I can offer is to say that you need to remember how it feels when you're losing compared to how you feel now. Or, to borrow a phrase from Nike, - Just do it.
Lots of people fall of the wagon. Just don't let the wagon drag you around! Get up and get back on - IMMEDIATELY. Life is made up of single choices. If one is bad - oh, well. If you let strings of bad choices run your life, you're doomed to the results of those bad choices. Don't let one bad choice wreck the rest of the day / week / month / whatever. FIX IT AS SOON AS IT HAPPENS.
Now that you're back from vacation, you'll be able to get things straightened around quickly. It's ok to falter - just keep moving forward from here on out.
Life style change started on Jan 13, 2011. I was going to lose 100 pounds by Christmas.
I lost 93 pounds by Oct 1, 2011 and am holding there for now. We'll see what happens.
New goal: To maintain at about 160
Final Goal: To decide if I need to lose more
Just Keep On Keepin' On