So more and more, I think the Upside Down is Will's mindspace. The red place with lightning bolts is Henry's, so Henry literally landed in his own mindspace to begin with when he got through the portal, although there might be an indication that Henry's mindspace was infected with something before he was cast into it, maybe a manifestation of his anger or some such, hence why the mindflayer and demogorgons and tentacles were there already.
So Will ended up in his own mindspace as well, which is why it looks like Hawkins frozen in time on that day, and Vecna then infected it somehow, probably for the same reason Henry's own mind was infected by the mindflayer to begin with.
This might explain the darkness El ends up in when she is in sensory-deprivation mode; she hasn't created any world in her own mind so it's just dark and empty.
It can also explain why he puts his victims in a sensory-deprivation mode (floating, broken limbs and spine so they feel nothing, blind); it might be Vecna's way of casting them into their own mindspace, trapped, and then he might infect those as well. We might see Max's mindspace in S5?
I wonder if they'll retcon that Will actually fell off a cliff before he disappeared.
BTW, in S1, Hopper has a flashback of his daughter having some sort of panic attack. I always wondered if that was going to come back into play somehow.
Well, they aren't writing the spinoff, and The Talisman's story is structurally very different from ST. I don't really think you're going to need to worry about that.
Hopefully, I might read it, will be my first Stephen King story, I've liked some of the movies adapted from his books but have never been interested in reading his work for some reason.
