Siblings can be very mean to each other while growing up. It’s a normal, though difficult, part of life. It usually comes from jealousy or some competition for love and attention. Sometimes it is a way to relieve stress. Although it is painful at times, it can also be a valuable learning experience. Learning how to walk away from provocations and how to manage conflict are useful skills.
How the fighting is handled matters. Usually parents let siblings work it out on their own, as long as everyone is safe. You did the right thing to walk away. There is no pay off for your sister if you don’t let her insults bother you. You figured that out by yourself.
But if the kids are hurt by their fighting, then it is up to parents to help their kids learn those important skills for getting along with other people. It was not helpful for your mother to support your sister in being mean. She probably didn’t realize that was what she was doing. She may have just been trying to defuse the negative feelings. I hope you will talk to her about how it affected you so maybe she will be more sensitive to your feelings in the future.
As for the anxiety attack: It hurt because your sister was hurtful. Your defenses were also compromised by lack of sleep and too much caffeine. Of course, you were upset. Any sensitive person would be.
But if those “attacks” happen frequently, you may need some additional help to learn how to handle conflict and bullying. The easiest thing to do is to read about conflict resolutions skills. If that isn’t helpful enough, a few sessions with a counselor might give you the practice you need to be less reactive.
I wish you well.