Doppler Question

I know I'm not supposed to be using a Doppler for the exact reason I'm posting. it causes unnecessary anxiety but I had a question anyways.

I am currently 10+3 and I actually have heard the babies heartbeat it sounded just like horses galloping and the Doppler picked up the heart rate. That's my problem is 2 days ago it was 182 and today it was only 167. I am freaking out that it would change that much in two days. Should I be worried something is wrong?