Dreaming is mainly caused by three aspects: excessive thinking and thinking during the day, some images in daily life can be presented in dreams, and dreaming in the subconscious becomes an unconscious activity.
When people think too much about some things or miss some people too much during the day, it is easy to dream after falling asleep, which is what people usually call "thinking day and night". For example, because I miss my deceased relatives too much during the day, it is easy to dream about my loved ones I miss during the day after falling asleep; For another example, when a person likes another person, he will always be obsessed with it, and it is easy to dream about this person in his sleep.