My girl recently have being shaking her head side to side when she was put on playpen.

It only happens after her morning feed @ about 6am where I will put her to sleep on bed. Before that, I have put her on sarong for the night and on bed after her morning feed.

She will shake her head side to side and sometimes quite vigorous. Not sure why she did this. She will have this shaking problem ONLY in the morning. Thruout the day, she dont't do that. Pretty strange.

Can someone please advise me why she did this? Thanks in advance.