Yup, I definitely have. During the summer, when I don't have to wake up for school, my sleep schedule goes straight to hell. Right now I sleep about 14 hours a day, scattered in little naps. I'm up most of the night, and asleep half the day, so my REM cycles are fragmented and I rarely get dreams worth remembering. And all attempts I make to get back into a regular cycle fail, since I'm not forced into going to school at 7:00 in the morning...
Well, I guess I haven't really lost the enthusiasm though, I just have a hard time finding an ideal time to attempt an LD. I still try WILDs most nights (or days), and I get the occasional DILD, but not as often as during the school year.