Never seen this behaviour before...

Hi, my 14 y.o keeps doing these confusing movements. I believe it's not stimming. 

Anyway, they happen quite a bit and I've only seen them recently. She told me that when cooking in school the other day, she was bursting with energy and when pouring ingredients her hands kept jolting and flour went everywhere. I didn't think too much of it at the time but now I'm getting a bit worried. 

Her neck keeps 'flopping' down out of the blue and sometimes if she's sitting her top half will flop and then she'll sit up again. Her arms/hands are clenched/tense and will usually punch anything near her. When this happens she'll say 'oh,whoops or sorry'. It's kind of worrying since I don't know what is happening but sometimes she's in shock and confused why it happens. 

Is this because she's excited and can't keep it inside her? What can I do? 

Thanks x