I often have this dream, but it's nothing. A few times I took the exam the next day, but the problem was either great or the study pressure was too great. Maybe you were thinking about the exam before going to bed one day, maybe unconsciously, maybe consciously. Dreaming is what you think before going to bed and it turns into a dream. Don't worry and have a good rest. Maybe things will get better. Others say that everyone only dreams every day.
Have a good rest, give yourself a holiday, play games, read books and listen to music, all of which are good methods. Just relax when you are under great pressure to study.