I've lost 17 pounds in 27 days & i'm not starving? Is it safe?

I was 293 about a month ago. I weighed myself and am now 276! I decided to change my lifestyle for good and lose weight the hard way with good dieting (1200 cal diet) and exercise. I am on a program called INSANITY. I watch what i eat and record it at all times. Salads, turkey sandwiches with the weight watchers wheat bread. I don't drink Sodas or juice anymore only drink water (about 10 cups a day) and skim milk for protein shakes and rarely use it to eat (special K) I don't always consume that because of all the sugar in it. I'm 276 pounds. I swear I haven't been starving myself. I'm just sweating like crazy trying to keep up with these exercises. Will my weight rebound? Is this safe? I heard safe is 2 to 3 pounds but my weight has been shedding like crazy..almost 1 pound a day..