I get really anxious when I go to chemistry because the teacher is one of those people who tries to get through as much as possible (talks really quick) and will call anyone out at random to answer the calculations
I'm always so anxious when I go into that class because I'm scared I'll answer it wrong and jesus forget it's happened so many times
I used to be the same way in my chemistry class, especially since a lot of chemistry at the level I was at consisted of maths knowledge, in balancing equations.
I'm not bad at maths as a whole, I just struggle with mental arithmetic, and if I'm not there with a pen & paper or a calculator, I'm struggling with even fairly basic equations. And of course, 9 times out of 10 the chemistry teacher is asking questions to do with balancing equations.
My advice though would be to talk to your teacher after class in private, and explain that you're having difficulty with answering sudden questions and it's making you rather nervous. And if you need help with chemistry altogether, then ask your teacher. If they're going too fast for you, they might not be able to adjust their teaching style, but they may be able to help you go over what you've learnt in after-class revision sessions.
Don't just sit there in silence, even if you're scared of your teacher.
I was absolutely terrified of my first year AS Chemistry teacher (she had a thick South African accent and a temper), and I wouldn't ask for help when I could've benefited, and I ended up with a grade C for my AS.
THen the next year I had a new teacher, who wasn't frightening, but was really rude and I swore she picked on me. She asked me if I wanted help, and I think mostly out of spite/pride I said I was fine, and then my efforts slacked. Eventually she stopped caring, basically said to my face that I would never be a chemist (or pharmacist as I was interested in at the time), and that was it. I didn't give a stuff anymore and started skipping lessons, among other things.
I ended up having wasted 2 years of college, and came out with a Grade E Chemistry A Level. It wasn't smart of me.
And all I had to do was ask a teacher for help, rather than sit there in fear or trying to spite my teachers.