Baby head shaking?

Does anyone baby do this? My daughter is almost 7 months and she shakes her head up and down like a yes motion. It’s honestly scary to see because she started it out of no where and I’m clueless on why. I called her doctor but she wasn’t in so I’m still waiting to hear from her, I figured I’d reach out to all moms on here too. I’ve read things that it’s normal but then there’s a possibility that it’s not and it’s literally brought me to tears fearing something is wrong with her.