I get the post con depression too. But I usually deal with it by pouring over the thousands of pictures and hundreds of hours of videos posted on the net. And of course getting ready for the next con!
I usually read and/or talk to people to pass the time. And since lines are a way of life at Otakon, I'm always sure to bring a bottle of water and some cereal bars so I don't die. In the end, I usually lose a few pounds by the end of the weekend!