Lost 15lbs in the past 22 days?!

So I haven't actually worked out in two weeks.... but still riding my bike to and from work. Ive been training off and on over those past two weeks and mentally Im drained when I get home so I've been sleeping lots instead of strength training. It is what it is. haha Trying to get myself into a routine once training is done.

At work in August, our office did a health challenge based on pounds lost (like the biggest loser). I weighed myself for the first time since I had my son in Sept 2017. I weighed 183lbs on August 1 and when we weighed in on August 31st, I was 179lbs. During that time I did FB workouts, 4-5 times a week, and only 30-40 min strength videos unless I didn't bike that day then I'd do HIIT.

Today, out of curiosity, I decided to weigh myself at my mother in law's and I weighed 165lbs. Confirmed that the scale is accurate as my mother has weighed in recently with her doc and was the same as her scale at home.

is it weird that I'm kinda sad about it cause I'm pretty sure Im losing muscle :(