For me, it would be the university and a session when I had to carry over 3 different courses. If I had failed another making it 4 courses, I would have been expelled and I would have to start all over again. I completely lost focus that semester and it affected my grades very bad.
I was bullied quite well but it passed at some point. The worst academic session experience I had was in one of my online classes on zoom. I couldn't understand anything the teacher was going on about for house. In fact, I slept throughout the whole session.