Thanks LDG, thanks Libby.

I really appreciate the reassurance.
I sent a message to my vet but they're shut on Sundays- the nurses go in to look after the animals but they don't take any calls. So I'll keep doing what I have been and speak to them Monday morning.

the_food_lady - I am absolutely floored. x.o Are you serious??? They put ANTIFREEZE in catfood??? I don't want to swear, but holy ****!!!!
I've just gone and thrown out all the food that I bought before she got sick... thankfully I haven't fed her any of it because she's been eating kitten food and other high-fat food instead of her normal, but... wow! She was eating a mixture of Dine and Whiskas food (I know it's cheap food, but I'm a student and at the moment I'm unemployed as well... so I couldn't afford to buy really top shelf food. x.o) as well as some home-brand cat biscuits. The only treats she had was Greenies, but not for a while before this happened.
I do have dogs, but they live at my parent's house. There's no way she could have got into my medications, either- I keep them locked up and firmly out of her way. The same with all chemicals and cleaning products.
Having said that, of course, she got outside a couple of times just before this happened... so I don't know what she could have got into out there. She's never going outside again, that's for sure! And I'm going to make a note of things I should look out for on the ingredients of cat food packets. I just... maybe a bit naively... assumed that the stuff they put in cat food WOULDN'T POISON THEM! D: