It happens but you will bounce back. you just have to have time. For me, the last two trips (a large family trip August 2011 and solo trip May 2012) I just could not get in the spirit. There was no "OMG 10 days to go!" and I didn't even start packing till like the night before. I don't know if it was because, for the family trip, I was going with some dramatic family members and just wasn't up for dealing with that and then the may trip was supposed to go see Davy Jones, when he died, any excitement for that trip died too. But once I got there, I was all Disneyfied again.
I think it can be the stress or the idea of the amount of work it takes to plan. for us, we go once a year and though you want to start planning as soon as you land back home; you really can't make reservations for a few months. My suggestion would be get home, enjoy the memories from your trip but don't think about future trips until your able to make actual plans (flights/hotels). That may help.
It is also a good idea to go other places too. I have been going yearly since 2006 and am only now starting to feel the urge to go somewhere else. Maybe go to Washington for a Phillie's/Nationals game or even go to Hawaii. I am preparing a weekend trip to a Monkees convention now, lol
I am finding that for my up and coming trip this Easter, I am all kinds of excited. I am counting down, watching Disney movies, listening to music at work, prepping what I am going to wear. I don't know why all of a sudden I am so ready but it may be because I haven't been there in a while and have done other non Disney things throughout the year. So the break helps. Sometimes doing something different gives you time to appreciate why you love Disney. Not saying other places are bad and Disney is the only vacation spot...just saying...absence makes the heart grow fonder.