Every people need to have a better sleep to rest before working and learning, making them more comfortable and feel relaxing. But that can't prevent them from having nightmares. I have had nightmares twice. One of the worst one happened only a few years ago, that made me go crazy and anxious. It was about failling the simplest English exam in school and I was punished because of that ( of course having a low mark in exams can't cause punishments, but this dream is weird and a bit awful ). The punishment was really terrible, as it forced me not to go to school for the whole course! Luckily, I don't often have nightmares in the evening, because I always have sweet dreams.