I had a nightmare. Should I be worried that it was a sign that I did some terrible thing that would deserve the kind of punishment I had in the dream? Also, what do we know about dreams? I’ve heard that when you go to sleep, your soul goes up to heaven and it goes through your next day and comes back into you to guide you through your day, but when I tell that to people they tell me its a really far fetched idea…
Regarding your dream, you’re 100% correct in disregarding the message or symbolism in your dream. The Talmud tells us that there is no dream that does not include in it some falsehood. Since we do not have the means to determine which part is false, we must not attribute any significance to ANY part of the dream.
There is, however, a distinction made for those on a higher spiritual plane – those that are more “in tune” with their souls (i.e. in earlier times, or for unique individuals in each generation) that do have significant dreams. There is even a “ceremony” that one might undergo if he experiences a shocking or tragic dream called “HaTavas Chalom”. However, many contemporary authorities state that such occurrences are rarities insofar as the spiritual level of people in our times has declined significantly vis-a-vis earlier periods in history.
Regarding your second query, there is much written on the topic of dreams in general and it is beyond the scope of this response to sufficiently cover all aspects. However, let me leave you with one core notion.
In his classic work Derech HaShem, Rabbi Moshe Chaim Luzzato dedicates a portion to describing dreams. Distilled to its essence, he breaks down a person’s soul into 5 components. They are: (a)Nefesh (b)Ruach (c)Neshama (d)Chaya (e)Yichida. Without going into too much detail, the Nefesh is the part of the soul that is closest relating to the body of man, while the Yichida is the part that is closest relating to G-d, or to spiritual essence. When one goes to sleep at night, 3/5 of his soul ascend to heaven while the 2/5 that are left remain down below, keeping the body “alive”. The upper 3 parts get “recharged” in heaven and are also privy to the goings on up there. It is for this reason that, depending on the spiritual level of the soul, one can be “told” about future events in his dream. It is in this sense that the Talmud refers to a dream as being 1/60 of prophecy. Of course, it should be stated that one is not bound by his dreams for the reason mentioned at the beginning of this response. Additionally, one always is given free choice to determine his actions – dreams notwithstanding.