This one is admittedly based on the idea of a short story I wrote years ago. Basically our characters wake up in something akin to a ward. Psych ward, medical ward, whatever. Somewhere of that sort. Looks very sterile and professional.

they wake up there with no recollection of what it is that happened, how they got there, etc.

They find out that it was thanks to someone named 'Riley' that they are there. Riley manages to convince everyone else that they are there willingly, but ... they know they aren't.

He's collecting people [all of which being humanoid, but can be non-human. Sirens, merfolk, etc is perfectly A-OK] to try and contain something.

I don’t know if this one would work, but it was something that crossed my mind.
One of our characters was attacked, rendered in a coma, and may very well never wake. The other character knows they have information, they have to. There is nothing to go on for WHO is responsible for the attack. No leads, no nothing.

Said character then researches what to do. Finds a magic based means to help.

After it’s set up, they are then put into a medically induced come right next to the other character… and their mentally enters the other.

The victim though, does not have a very pleasant head. The damage which was due to both physical damage, and an unknown aspect - which was magic - had made her head essentially a mine field.

And the other character has to find them within their own head, and help them get out of there.