Dreaming is mainly caused by the following situations:
First, a lot of mental work or contact with things that leave a deep impression on you will lead to the active state of brain cells, which will increase the activity of the subconscious mind and lead to the emergence of dreams.
Second, the influence of the external environment will also increase the chances of dreaming. For example, when the outside temperature suddenly drops and there is a lot of noise, it will cause the body to send a bad signal to the brain and it is easy to have nightmares.