Regarding “xenomnesia”: It’s possible you have a mental connection with a character. Or empathic. Some kind of connection that let you share thoughts or memories. Or maybe even: Is there any kind of otherkin “vessel” concept in use? Channeling someone? Or having them give you thoughts/memories somehow? (I’m an empath, and I know a lot of my synpath [non-kin, but very deeply understanding] connections have this effect on me, especially my primary “soulbond”.)

Absolutely. There’s lots of reasons that this phenomenon could occur. Fictionflickers come to mind too as a possible source for xenomnesia.