Reliving memories and sharing them with loved ones/enemies is great.
Now there's ALSO an option to share things that never happened or couldn't possibly have happened with people.
The Short Version You can now relive memories your character never had or couldn't possibly have had such as having a character your character remembers dying attend their own funeral or showing up before they were born or AUs with player permission.
What: The Memories plot from the Test Drive Meme, except now you can have AU versions or things that couldn't possible have happened by mixing your character's memories together. But these memories are extremely unstable and nothing can be brought out of them.
Why: Because D is going to make a truly inadvisable choice and cut his way out of a memory rather than deal with it properly.
How: Cutting ones way out of a memory dimension is a bad idea and D is going to cause ripples when he does that, but because he did his magic dimension-cutting in a memory, it's only going to ripple across memories.
Reading books isn't necessary for the messed up memories. Being near a book and having thoughts at the wrong moment when a metaphysical ripple is passing by is enough for people who want to play with it but whose characters don't like to read or wouldn't be nosy enough.
For How Long: The ripples will continue for a few weeks before they naturally resolve.
Characters can end a faulty memory on their own by recounting what really happened to another sleeper either in the memory or keep it from coming back by sharing the 'truth' in public.