Why am I suddenly having vivid nightmares about a book I read decades ago?

I had a series of nightmares about "Gollums" from Robert Jordans' "The Wheel of Time" series. I remember, I think, they are first introduced in book 6, "The Lord of Chaos". They are invincible to physical damage and invincible to magical damage (The One Power) and can only be hurt by Matt Cauthon's anti-magical Fox Head Medallion, at least in the books. They are basically shape changing vampires in addition to all of this.

So anyway, all night last night I dreamed about being attacked by these damned things, and several murders committed by them, and I have no clue why. In the dream, with help from another person, I was actually able to kill one of the damned things, which i found somehow encouraging, but there were more than one of them.

What do you think this means?

I have not read any of the books in this series in over 20 years, but I did order 3 books to finish reading the series a couple weeks ago. I just haven't started reading them yet. Why would I suddenly have nightmares about an obscure scene from these books which I haven't read in 20+ years?

Why am I suddenly having vivid nightmares about a book I read decades ago?
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