11 month old suddenly falling backwards

My LO has been confidently sitting since she was six months but recently has started falling backwards. I can’t work out if she’s doing it deliberately or accidentally but either way she sometimes hits her back and head and gets upset. She can’t crawl, has just started rolling front to back and can stand with assistance.

I’m suspecting she’s either trying to activate different muscles to try and move, resulting in pushing herself backwards or maybe has balance problems as she’s coming down with a bug.

Have any of you seen anything similar? I don’t know whether to be worried or not. She seems herself in every other way except for a congested nose. It’s just difficult because she’s at nursery tomorrow as I go back to work and I don’t want her injuring herself by constantly falling over.

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