Just because it's easy doesn't mean it didn't worry you. I recall significant amounts of stress about passing tests on subjects I never got lower than an 80% on. Just always expecting to do the test, thinking I did well, and then get slapped with a fail. Never happened, still worried me.
I'd honestly not be surprised if the whole "dreams about school" thing turns out to be world-wide low grade PTSD.
For me, both elementary and high school were easy. I would do a minimal amount of work, show up to the exam and get maximum marks. Exams weren't especially stressful.
As a stereotypical school nerd, PE was stressful though - I do remember lots of anxiety being asked to jump the vaulting horse, do somersaults, handstands, and that kind of things I wasn't able to do.
And yet, I regularly dream about not having passed some non-PE high-school subject and having to retake the exam and/or go to class (even when these subjects were easy for me) and don't dream about PE.