Weight surprise

I weighed 202 lbs on the doctor's scale at noon today.  That's 13 lbs less than 10 days ago.  (I haven't had an actually working scale at home for a long time, so I only check my weight at the doctor's.)  This actually concerns me a bit.  When I was 215 last time I was there, it was a pleasant surprise but reasonable, down 6 lbs from two weeks before that.  The only real change in my eating habits has been that I've been sticking to my eating guidelines much better than usual.  I'm eating all my meals, eating normal amounts at those meals, and enjoying them normally; I just seem to have pretty much lost the urge to snack.  I've been keeping myself busy, but I haven't suddenly started running 10 miles every day.  I feel fine.  I'm just wondering if I need to be worried.