Our cat was playing and acting totally normal and then started hissing and won't move. She just sits in places she never sits at/in and when scared usually runs away and hides but now she is just refusing to move. Please help!

Refusing or unable? Is her sitting position a little "off" or "weird"?
I don't know that I've ever seen a cat flatly refuse to move if they have the urge to get away or to something.
If she is, in fact unable to move, and use her back end, she could have a serious problem.
Saddle thrombus or back injury come to mind. These are just guesses.
In any case if she is in unable to walk she needs to see a vet soon.

She could be unable to move her back and if she doesn't move soon u shold take her to a vet asap