Dreams: Angelic or Demonic?

Source: Rabbi Shelomo Almoli - Dream Interpretation from Classical Jewish Sources

The essential characteristic of an angelic dream is that it is orderly, with no extraneous material mixed in.  Furthermore, the dreamer should not be panicked or frightened at the time of dreaming, and he must see himself as though truly awake in the dream.  If all these conditions are fulfilled, you may be certain that the dream is true, and that it comes through an angel and is a one-sixtieth part of prophecy. [Berakhot 57a]

However, a dream which comes by means of a demon is quite different.  The demon stands near the person as he dozes and whispers frightening words, a concoction of many things, into his ears.  This arouses frightening images in the dozer's mind; his heart beats wildly and he awakes in a panic.  [literally the great panic awakens him].  

The demons remain at his side, rejoicing and toying with his mind in order to frighten him, when he falls asleep they begin again.  After this happens several times [after he awakens from a doze and finally decides to go to sleep again for the night], he finally begins preparing for bed by reciting the Keri'at Shema prayer, or deals with them some other way.  He awakens and recites ''Unclean, unclean! Flee from here!'' three times.  At that, the demon will go on his way, and the sleeper will be able to rest, secure from such dreams.  

Below is a lecture on Dreams from Rabbi Alon Anava from 2018.