Day 3 of 40 day water fast and I already lost 20lb. Should I be worried?

I started my Water Fast on the 26th of may 2017. As I am typing this thread, im currently on my 4th day. My starting weight before the fast was 280lb. Despite being almost 300lb, I don't look like I weigh that much, maybe its because I'm 6ft tall. On my 3rd day, I went to use the bathroom then got on the scale and my weight was set to 260lb. I was really shocked because I thought maybe I broke the scale. I kept getting on and off the scale thinking something is wrong, how did I lose 20lb in 3 days?. It could be possible that that 20lb was water weight but I find that very hard to believe. A little back story: when I was younger i use to be skinny until I moved to U.S and 12 years later, I got fat. Maybe its just my skinny genes being unleashed?? I can post pics for proof if necessary?