The time in the park does fly by too fast, and I always find myself bemoaning the fact that 'half the trip is over' midway through...and my husband always says we have a whole half a trip left. That helps until the last day.
So, coming home is even worse.
So, I try to start planning our next trip ASAP, even if I don't have a firm date. I have a sophisticated system of tracking our trips- a legal size envelope- and I make notes about what we want to see next time. As I peruse blogs & Disney-related websites, including the Disney blog, I add to it. I listen to park music and loops, and watch park videos.
But all that can't take the blues away, so I suggest you plan to do something fun at home shortly after returning and later on. Doesn't have to be anything big or expensive, just fun and something to look forward to.