A bit of explaining before.

I was an Ace Student. I was getting perfect grades, I was easily understanding all that the teachers were teaching to us. I was heading towards a shining career in life. And then 11th grade rolled in. (I grew up in Romania. There you do 8 years of... Middle School? Then 4 years of High School but only the first two years are mandatory)

I came out of that summer an absolute mess. I have no fucking idea what happened but I could no longer grasp even the most basic lessons and concepts. From the best, I was in danger of repeating 11th and 12th grades due to failing at

Every

Single

Test

Tests became an absolute nightmare. I dreaded all tests from 11th grade on.

I had to force myself to study anything and memorise all the theory I could. I barely passed but flunked my romanian final exam (thankfully I passed after contesting my grade.

I became even more depressed that I already was due to that and now I constantly doubt myself of anything I know, do, say, etc.

PS Sorry if this doesn't fit OP's question and/or if I made any mistakes while writing this.