Okay, good news! Thankfully, I looked up (googled) my exact problem and found that by restarting my browser fixed the issue. My apologies for freaking out, it's just I'd never come across this before! I only hope this helps someone in the future. I did take a screenshot of what the icon looked like (non-moving, of course). So I can say I've answered my question, and no longer need help...but glad to know where to go to!
Elizabeth
I have had the same problem twice now. I just assumed it's this terrible laptop I'm using. Is your computer slow or fast?