Yeahh, I'm with surferchick on this one-- it definitely happens to all of us, and the way to get through is try to keep your head up, even when you don't feel like swimming.
I have a friend who runs cross country track, and she used to tell me that part way through her run, she would always hit a slump where it hurt to keep running. She used to say of this, "when the walls are closing in, the only thing to do is fight the roof!" As a result "fight the roof!" has become my little mantra for when I feel that I can't keep going on my weightloss journey.
Also, I keep around a little string bikini that I plan to wear at the beach with my boo this summer... putting that on makes me want to look fabulous, and renews my resolve.
Good luck! You can do this!!