My friend physically hurts me on purpose, what should i do?

This has been a problem for a couple months, I (16F) and my friend (17F) been friends for just over three years so we are very comfortable with each other. Our humour has always been satirical comments, taking the piss etc.

The first time she hurt me was after i made one of these comments (it was nothing insane, in fact she’s said it to me many times) in which she grabbed my head and slammed it into the desk. It really hurt, and she never said sorry, but i didn’t want to bring it up. I just assumed she didn’t mean to do it that hard and i let her off.

After that i was careful what i said to her because i didn’t want to upset her and was worried maybe the joke was taken too far.

Then recentlyshe started holding a grudge against me, and almost everything I said or did was a problem. Our friend group have noticed this and also think the grudge is very unwarranted. This is when she starts hurting me over the simplest things (borrowing a ruler, asking for help) again; slamming my head, pinning my hand and banging her fist onto it, bending my fingers and arms, hitting me (which resulted in bruises).

Then today, she grabbed my hand whilst holding a pair of scissors which (accidentally?) resulted in a gash on my palm. She did say sorry but then continued to say i deserved it to my other friends.

I cant tell if it’s a joke anymore, and i know i’ll make it awkward by bringing it up. Plus the ‘injuries’ aren’t even that serious and i don’t wanna seem like a wuss. What should I do?