“@MDG: Interesting! Are you going to keep the commitment?”
I have not done anything in regards to that dream.
There are differences in sources of dreams. In my case, it was something that was on my mind, so having a dream about it is no Chiddush (see B’rachot, around daf 56, concerning the kings asking what they will see in a dream).
Whereas in the case of the recent Dam Yomi sugya in Nedarim, where a person has a dream of being in Cherem, that person should get out of cherem somehow (by getting 10 learners to absolve). That dream is considered sign from Shamayim. It seems to me that no one thinks about being in Cherem during the day and dreams about it at night. That’s why we can assume it’s min Hashamayim.
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“And don’t be fooled by “choshuv looking”!”
I have a book on dream interpretation which says that the Shadim that bring “bad” dreams can sometimes come in the guise of tsaddikim. That way they befriend and help at first, so that they can lead astray later.
The way to hold off the Shadim is to say Sh’ma Yisrael and Baruch Shem every time you go to sleep. The passuk of “Biyadicha Afkeed…” also works (see B’rachot top 5a). If you wake up in the middle, you lose the Shemira, and you need to say them/it again to regain Shemira.