This can mean many things. The letter could be from a relative that is allready dead, and this relative is trying to contact you. If it was a decent, friendly letter they may be trying too see if you are okay, and that you are still remembering them. If it is a very short sentenced letter, or may have threats in, this person may be wanting to take revenge.
Another posibility may be that someone in your family, or close to you may shortly pass away, and their spirit is trying to contact you telling you not to be woried and they will allways look over you.
The most comman posibility may be you just were having a bad dream, and it mean nothing. Maybe before you went to sleep you were thinking about a dead relative and letters. Or quite possibly you were thinking about a film of tv program to do with your dream.
Dreams communicate through symbols and metaphors. Usually, death in dreams represents change; the end of one stage of life and the beginning of something new. This dream suggests that information from the past, specifically from something or someone who is no longer a part of your life, is going to create changes for you.
A memory of a person dead but not forgotten.
If the question is referring to a dream about a dead person and a dead fish, it could mean that the dreamer is feeling rather hopeless. Beyond that general suggestion, the dream's meaning would depend on who the dead person is and what relationship they have to the dreamer.
if you dream of someone that is alive and is dead in your dream then that mean that that the person will have a long life
It is often said that if you dream of a dead person dying again it means someone you know is pregnant. Of course, it could just mean that you are missing the person that died.
The dead person is a symbol of the past. The dream may mean that you are ready to "kiss" the past goodbye. You are ready to let go and move on with your own life.
If the person in this dream has recently died, the dream might be part of the grieving process. The dream represents the dreamer's difficulty in accepting the reality of the person's death. In the dream, "you" are the intellect, which understands that the person is dead, and "other people" represent the emotions, memories, and other aspects of the Self.
Dreaming is a continuation of a person's thoughts throughout the day. If you dream about a dead husband, you are just remembering him, and missing him.
It probably means you are dehydrated
Dreams are just dreams and do not "mean" anything.
That the dead person is probably someone you know, and that person is still around watching you and guiding you.
This suggests that the dreamer is coming to accept the reality of that person's death.
You feel disconnected from that person, either emotionally or physically.