Sudden weight loss right after start of workout--scary or effective?

last thursday i started a new exercise regimen after being fairly inactive for an extended period of time. (gotta love the confined office jobs.) 10 minutes on the elliptical, 15 on the treadmill. also light weights for the arms; 12 reps four ways. this makes for a little under 30 minutes a day. i have combined this with drinking 64 oz of water a day, and cutting down on bad foods. last monday at the doctor's office i clocked in at 166; i went home to my own scale and it was the same thing. 166. this morning, after the 30-minute regimen going since thursday, i checked the scale and i was 157. my clothes aren't really that much looser. should i be panicked? or is this a good thing? thank you!