In-dream memory infodumps?
Are made-up memories that come suddenly in a dream so common?
Like you're dreaming you're in a fancy ballroom then you see some sketchy rando, and you think: "Oh, that's Liam, the (nonexistant) brother-in-law of my sister, I owe him money but he's not gonna come claim it because I know he's cheating on his wife with his bodyguard".
Or you enter "your house", which you've never seen before (as the matter of fact it doesn't even exist in real life, you've lived in a condo since you were born) and you find the pruning shears left by your grandpa in his deathbed (he's alive IRL) exactly where you left them, and go get some apricots from the tree your aunt and you planted when you were little (you never planted a tree and you don't have aunts, even).
Why do you think this happens?