hi huishan, there are many reasons your baby could be doing this. it could be she is having nightmares, and yes, it is possible for small babies to have bad dreams too, or dreams that make them uncomfortable. my baby also used to do like this and i would immediately start to lightly rub her back or legs and hold her finger. i used to talk to her soothingly, telling her i love her and it is time to sleep.
on the other hand, she may be starting her teething phase. to make sure she does not have any pain or discomfort in the gums, you can massage her gums lightly by wrapping a clean cloth on your little finger.
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