What happens if I exceed the request limit on the free plan?

Hello! Sorry for noob question.

Right now, I'm on the free plan, and I have some pages and one worker that uses email routing to send an email. What would happen if I got ddos and exceeded the free request limit? Do I get billed, or does it just stop working? If I got billed, can I change it so it just stops working?

Thanks in advance.