The Sages formulated a prayer to be recited before sleep, in which one requests that he not experience any disturbing or frightening dreams. They also composed a prayer for one who already experienced a troubling dream.

Rav Yehuda said that Rav said: Three matters require God’s mercy [to facilitate them]: a good king, a good year, and a good dream….

Ameimar and Mar Zutra and Rav Ashi were sitting together. They said: Let each and every one of us say something that the other has not heard. One of them began, saying: Someone who saw a dream and does not understand what he saw should stand before the priests at the time that they raise their hands for the Priestly Blessing and recite this:

Master of the Universe, I am Yours and my dreams are Yours, I dreamed a dream and I do not understand what it is. Whether I have dreamed about myself, whether my friends have dreamed about me, or whether I have dreamed about others: If they are good, strengthen them and reinforce them like the dreams of Joseph, and if the dreams require healing, heal them like the sweetening of the bitter waters of Mara by Moses our teacher, and like Miriam from her leprosy, and like [King] Hizkiya from his illness, and like the bitter waters of Jericho by [the prophet] Elisha. Just as You transformed the curse of Bilam the wicked into a blessing, so too, transform for me all my dreams for the best.

He concludes his prayer together with the priests, so that the congregation responds amen [both to the blessing of the priests and to his individual request]. If he is not able to recite that entire formula, he should recite this: Majestic One on High, who dwells in might, You are peace and Your name is Peace. May it be Your will that You bestow peace on us.

If a person sees in his dream as though a sword is cutting his thigh, what should he do? He should rise early to go to the synagogue and stand before the priests and listen to the Priestly Blessing, and no evil matter will harm him.

One who goes to sleep on his bed recites from Shema Yisrael to Vehaya im shamoa. Then he recites [the following formula]: Blessed are You, Lord our God, King of the Universe, who makes the bands of sleep fall on my eyes and slumber on my eyelids, and illuminates the pupil of the eye. May it be Your will, Lord my God, that You have me lie down in peace and give me my portion in Your Torah, and accustom me to mitzvot and do not accustom me to transgression, and do not lead me into error, or into iniquity, or into temptation, or into disgrace. May the good inclination have dominion over me, and may the evil inclination not have dominion over me. Save me from an evil mishap and evil diseases. Let neither bad dreams nor troubling thoughts disturb me. May my bed be flawless before You, and enlighten my eyes lest I sleep to death. Blessed are You, Lord, who gives light to the whole world in His glory. (Berakhot 55a; Bemidbar Rabba 11; Berakhot 60b)