How weird...I just posted in the "confess your sins" thread that the last two times I left DL, as we were walking out of the park I started crying. I couldn't help it, and I felt so stupid. My DS 15 noticed and got really concerned, saying, "Hey, Mom, what's wrong? Are you ok?" Embarrassed, I told him I was just so sad to be leaving, and he gave me a big hug to comfort me.
One way I deal with the post vacation blues is to get prints made of our pics ASAP (and we take a million pics!) and scrapbook them. I put a lot of paper mementos in my scrapbooks, too -- menu copies, postcards, tickets, certificates, stickers they give you to wear on your birthday or like the "I braved the TOT" one I earned (I peeled them carefully off my shirt and stuck them to scraps of paper to take them home), maps, etc. It is a lot of fun to make the pages, and when I go back and look at them, it's like re-living our trip.