What could be causing my overly vivid dreams the past few nights?

It seems that for the past week I haven't been getting the restful sleep I used to be getting, though part of this is due to a slight modification of what time I was waking up over the weekend. (I am used to sleeping till around 10 or 10:30, but over the weekend had to get up around 8)...however to compensate I went to bed a little earlier. Anyway, I can remember for the past 2 or 3 nights, having very vivid dreams....dreams that I can tell in great detail and still remember right now. Normally I wouldn't mind recalling dreams, as it's something I do periodically, but never as vivid as these, and also, I think they are causing me to feel less rested when I wake in the morning. Any ideas what could be wrong? Is it just lack of sleep, too much on my mind, or what?