Are As mocks really important?

Just wondering, because I have mocks after the Christmas holidays and I'm freaking out...

No, they're not "really important". There aren't any significant penalties for failing, not on paper anyway. However, it is still worth taking them semi-seriously because the mocks exist for your benefit - they allow you to see where you're working at at the moment and what you need to do to improve. They can make you realise you need a kick up the backside or alternatively if you do well (which is why it's not a bad idea to revise for them), it can be a huge morale boost. Nevertheless, whilst I would recommend people do work in preparation for them, even if you completely flop then it's not the end of the world. You might get a stern word from your teacher but it's definitely not going to have any impact on your actual AS grades/predicted A2 grades/university application.