Ri Kara citing Brachos 10b: If one has a dream that he will die tomorrow, he should not despair from Hashem's mercy. (Maharsha - even though it is probably from a Shed, and totally false, he should be concerned lest it is from Hashem, and pray.)

Rav Sadya Gaon: When dreams, Havalim and many matters overpower, strengthen yourself in Yir'as Hashem.

Rashi: In spite of all that dreams, vain prophets and many words will tell you to separate from Hashem, do not heed them. Rather, fear Him!

Ibn Ezra #1: This is like Ki Ba ha'Chalom b'Rov Inyan" (2; when many matters are mixed in a dream, it is Hevel). However, fear Hashem in everything.

Ibn Ezra #2: See many dreams, and much folly, and speak much, just fear Hashem. I.e. you may say anything, unless it mentions Hashem (then you must be careful about what you say).

Rashbam: Via many dreams, follies and many words, people are lost from the world - "Lamah Yiktzof ha'Elokim?" (5)! Rather, fear Hashem, and do not increase words.

Rid: When dreams, Havalim and many matters come upon you, do not fear, that you will need to vow [for a merit to be saved from them]. Rather, fear Hashem and He will save you from all evil.

R. Avigdor citing Koheles Rabah: If you see bad dreams and evil decrees, save yourself via Tzedakah, Teshuvah and Tefilah - "va'Yikan'u Ami? va'Yispalelu vi'Yvakshu Fanai v'Yashuvu mi'Darcheihem ha'Ra'im" (Divrei ha'Yamim II, 7:14). Va'Yispalelu is Tefilah; vi'Yvakshu is Tzedakah; v'Yashuvu is Teshuvah. Immediately, "Eshma Min ha'Shamayim v'Eslach l'Chatasam" (ibid.) Some say that also fasting saves - "Ya'ancha Hashem b'Yom Tzarah" (Tehilim 20:2). Some say, also changing deed, name and place can save. This is the source for a Choleh to change his name. We find that it was decreed that Avram will not father, and Avraham fathered (Bereishis Rabah 44:10).

Seforno: I warned you against elaborating in Tefilah and against vows, lest you stumble in them. Both of them can occur via frightening dreams with many false imaginations. The dreamer thinks that he can evade [the evil that he saw] via many words in Tefilah and vows. This can occur also via Havalim - one prays in order to get excesses with improper purpose, or it can occur via excess words, which always lead to sin. Rather, fear Hashem and His great grandeur; consider the great danger if He is angry, and do not enter this danger.

Metzudas David: Do not be concerned for many dreams, sayings of Hevel and other matters ¹ . Rather, fear Hashem, and He will save you from all evil. The verse is abbreviated; the omission is understood.

Refer to 5:6:1:1-10.

Ri Kara: When your heart counsels you "Lehotzi Davar Lifnei ha'Elokim" (1), do not; rather, fear Him.