After stumbling upon references to Starswirl the Bearded's brief foray into the research of dreams, Twilight begins having frightening, morbid nightmares. What begins with skeptical curiosity about what Starswirl's research would have to say turns into a desperate plea for help as Twilight begins to doubt she is really dreaming.

Thanks to Pegasus_Jones for help with the title!
Links to fully-formatted versions of each letter are in the Author's Notes.