Babe, you can do this. You don't have to look at him. The DA's office will be there -- when I testified in a similar situation, they were super supportive. I'm sorry you didn't get more prior warning, and I'm sorry you don't have anyone to bring with you. Call the DA's office and ask them if they want the video -- I doubt they'd use it (it's from another event, and he's not on trial for being a general abuser and ********, he's on trial for one particular instance of hitting you.
The flashback you got was scary, right? I hate those. Tell you what though: They do go away. They get weaker. You will get to a point where you can even talk about what happened without flinching.
Testifying is a great way for you to stand up for yourself and say "I don't deserve being abused; I know I didn't deserve it; and I want the court to tell him he was wrong."