Bro kinda the same thing happened to me today. in history class my proffesor was asking me questions for a grade and i knew everything but i just couldnt get it out and i hmm'd a lot and i just said 'next question' everytime and in the end i got a D instead of a good grade and after the class ended i literally wanted to kill myself beacuse the day before that i was studying for like 5 hours straight so i did all that for nothing