Yep, women are natural worries - men have that "she'll be right attitude!"
Yesterday, i felt bubs move heaps, the most i have felt, but today, nothing! I think they just move positions alot. I have noticed that i will sometimes feel big movement, and then nothing for a day or so, and then movement again. So, it must just be changing position, and because i am only 21weeks, i try not to get to concerned if i dont feel it every day.