is my cat okay??

I have a 2, almost 3 year old orange tabby girl. She is very smart, and cuddly, and also very orange; but yesterday and today have seemed off.

Late last night my dad was walking in her direction and she started hissing, like, more than a few times and then she just seemed hyper-vigilant. she was also hissing and growling towards my moms cat, a big boy grey tabby who we've had for just about two years now. She has only ever hissed at the other cat after he comes back from vet appointments or when he first arrived.

I figured maybe she played too hard and maybe was overstimulated but even today she's been asleep most of the day and decided to bite and roll around on my blanket. I'm just very confused and scared that my cat is sick or something and am really hoping it might instead just be a fluke.

I have scheduled the first vet appointment I can with OHS, but its in march.

Any advice is helpful :3