Is it OK to have a significant drop in grades when moving from the Middle East to the EU?
Background: Some time ago, I've been working at a German university as an assistant in electrical engineering, and we had some students from Arab countries.
Generally, they were much better than the Germans in reproducing content they had learned, but had more difficulties than their colleages in applying that knowledge to the problems at hand. And the university valued knowledge application much higher than knowledge reproduction. So they had a hard time adopting to that different learning style.
Coming back to your question:
It might be that from a different cultural/educational background, you're used to a different style of learning than what the German university expects from you.
My best recommendation would be to seek contact to your professors and your colleage students, to find out what the professors expect / what the other students do differently. Try to find some colleages to form a learning group.
Your colleages are surely not brighter than you, they only have better adopted the learning style that the university expects (they grew up in the same educational system where they are studying now). Most probably, they'd have comparable problems when going to a Middle East university.