The first situation may be because of the bad movies you watched recently, which have some fragments that touch your sensitive nerves, which will lead to nightmares. For example, I have seen a movie about a female college student being abducted to a mountain village, and then all those nights were taken away by bad people. I really feel bad, and because of this, I will be very wary of strangers.

There is another situation, that is, you have read a lot of books recently or you are under great mental pressure because of the upcoming exam, so you will also have a lot of fantasies at this time. Usually we have a lot of pressure during the final exam, because after the final exam, you will face the summer vacation or winter vacation. Your grades will directly affect your happiness during this holiday, so many people will be very nervous at this time, and they can't sleep well and eat well every night. In your dream, you will feel that a monster is chasing you. In fact, this is a reflection of your inner desire to get rid of this situation.

There is another situation, that is, because something bad has happened to people around you, you may think it will happen to yourself. If you think too much, you will dream at night, so you will have nightmares.