Pekin duck neck problems?

[Myavia]

Hello! My 3 month old female Pekin keeps doing this head bob thing. It’s been going on for a little bit, but seems to be getting more frequent and more aggressive. She functions normally more than half of the time, but I’m concerned. Does anybody know what’s wrong?
Couldn’t attach video directly so posted it on YouTube -

 

[EverythingDucks]

I can't tell from the video but they usually bob their head when they're excited or 'flirting'.

 

[Myavia]

I can't tell from the video but they usually bob their head when they're excited or 'flirting'.

I’ve never had ducks before so I wasn’t sure. So that looks like a happy head bob and not a physical problem?