Folk tradition yoked weddings and funerals together long ago. The dictionaries and the proverb lore read the two by contraries in both directions, a dream wedding foretelling a death, a dream funeral a marriage, and the pairing was not arbitrary: both ceremonies take a person out of one state and deliver them into another, dressed and processed and witnessed, and the old Greek handbooks had already read marriage and death as images of one another on exactly that ground. The reading is a tradition's, not a fact, but it is one of the most persistent in the whole folk literature.
The psychological traditions kept the structure and dropped the omen. A wedding joins two parties into one household; read inwardly, in the Jungian manner, the dream marriage becomes a union of opposites within the dreamer, a reading that school took over from alchemy, whose texts imaged the work's completion as a royal marriage. Freud's tradition attended instead to whose wedding the dream stages and what wish or fear the staging serves.
Beneath both, the modern research reading is plainer: for the betrothed, wedding dreams, including unhappy ones, are ordinary rehearsal anxiety before a large and public undertaking. The dream is doing what dreams demonstrably do with any approaching performance, and needs no symbolism until that layer is exhausted.