Why am i losing a pound a day?

I use to be 293 i'm now 274 ever since I started Insanity 22 days ago. (Workout program) but i'm eating 1500 cals a day.. 5 small meals a day. Is this healthy? and will my weight rebound? I'm not starving myself.. the weight is just really coming off .. I'm really happy! but confused and scared of my weight rebounding because it's coming off so fast..