a fish that swims into your brain

You know those fish in the Amazon that swim into your dick while you're pissing?  Well, a quick little silver fish just swam into your brain when you opened it to the Maelstrom.

Now what?

I'm running a jungle-pocalypse and I really want to do this to my players when they fail an open-your-mind move, but the question is, what does a fish do once it's in your brain?

It ended up there, stuck, misled by the twinkling shines of your memories, very similar to those of the psychic plankton it feeds on... Now you can't seem to remember what color were the eyes of your little sister, who didn't make it past your childhood... What was her name? Wait a second, Are you sure she was a girl?

As most brain parasites it changes your behaviour in a way to make it more likely you're eaten by the primary host.

A whisper in the maelstrom and wonderful dreams of a paradise somewhere in the jungle. The paradise exists but it's only a paradise to the jungle mutants who dwell there and feed on those infected by the silver fish. The brains are eaten raw. The silver fish mature and reproduce inside the mutants and awful boils burst to release thousands of young silver fish.

The mutants might be welcoming and are possible naive as to their part in the parasites life-cycle. The urge to feed the infected to their own children becomes overwhelming and could be a mysterious tragedy even to themselves.

There's a party. Loud music, but it's a good kind of loud, drumming, singing, hollering, laughing. People dancing and making out all sorts of things. Maybe it's deep in the jungle, maybe it's in the maelstrom itself, but your buddies can't see it and oh if only they could and dang wouldn't it be so great if you could go there, like, right now?

Hell, just try talking to one of those crazy party-people, and it's like they totally get you, they totally get, like, the universe and gee your friends are looking at you funny but if only they saw it, they really should get a silverfish man.

Great ideas, thanks!  I think I'm going to use Krippler's idea.  I'll let you know how it goes.