This is because you have been affected by the horror plot after watching the horror movie and have developed psychological fear. These plots might make you think of death, ghosts, monsters, and other terrifying elements, causing you to feel uneasy and afraid. This fear may affect the quality of your sleep and make it difficult for you to fall asleep at night. I suggest you try relaxation techniques such as deep breathing, meditation, and gradual muscle relaxation to relieve your nervousness and anxiety. At the same time, you can also try to watch some other types of movies or read some light-hearted books to divert your attention and emotions.