nervousness during case interviews

I’ve done a good amount of casing this year for recruiting and I feel really confident in my frameworks, math, problem-solving skills etc

I had my first actual interview last week and I just got so nervous during the interview that I couldn’t do simple calculations. Like literally simple profitability stuff that I’ve done so many times, I just kept freaking out. Do you guys have any tips or help for this? My mind just goes blank when the actual interview starts