My mom hits me whenever she's mad. Sometimes the abuse can be really bad? What should I do?

You must ask her to stop beating her. Ask the reason she beats you. If she beats you just to relieve her stress, warn her that you may commit suicide that you are already yourself stressed. A mom loves her kid. She will get afraid and stop beating you. And you can do self-defence which only includes stopping her movements not beating her. So that way she can stop beating you. Also if you can help her with her stress she is suffering from, she will eventually stop. Maybe she is sad in her life.So I wish I was able to help you.