This event happened close to twenty years ago. I can check the exact date, but I don't think that's important. I had what is called a visitation dream. Like most people, when I've had a particularly dreamy night, I usually forget everything a few minutes after waking up.
My first wife and I divorced a few years previously, for reasons that I don't need to go into, but suffice to say, her personality slowly began to change as the years passed, and she became hostile, dishonest, and not nice to be with. Our family doctor described her personality as psychopathic.
She appeared in my dream with a message for me. It was a head and shoulders image with a dark background. I cannot recall any of her words, only that it was an apology. A sincere one. An apology for past behaviour and the unpleasantness she had caused during the last years of our marriage. This was certainly out of character for her. An apology from her for anything was something that I couldn't recall.
The dream made such a mark on me that I made a note of the date in my a appointment book. Something that I hadn't done before and haven't since. At the time I felt that it was a visitation dream (a term I learned of later), and that she had died suddenly, and I would probably soon get a call from our son to that effect. He was living with her at the time. He did call, but it was a year later. She had just died in a traffic accident, a year to the day after the dream.
Over the years I've replayed this event in my mind, and shared it with a couple of close friends. No explanation of course, except that it's a reminder to me, if one were needed, that there is a lot going on out there that we just don't understand.