omg found my baby's heartbeat on my doppler, but I listened for like 10 seconds and then I lost it? am I imagining things

So I have the angelsounds which I know it's not as good quality as the sonoline. I have heard my own heartbeat on both sides by my pelvic bone when I tried at 9 weeks + 6 days. I tried again today at 10 weeks + 1 and was almost about to give up when I caught something and sure thing it was different than my heartbeat much faster sounded like a train so right away I knew that was the baby. But i couldn't hear it after about 10 seconds. Now I'm sitting here wondering if I imagined it all lol 😩