I also recall seeing a TV show or movie or series where someone in a pool transports elsewhere. I could Google it and then I'd know if I'm recalling something I've seen or just think I am recalling it.
Isn't there some line of thought that there are something like 7 basic plots in all of literature? Or maybe just one - some kind of Hero's Journey? It's a normal day, then something happens to change the world of the protagonist, then they have to take action to overcome this. I guess people find it entertaining because they see themselves in it. Everyone continually has this plot in their own life.
As far as originality, we're seen the same issue in music. Someone borrows a riff or a lyric and builds it into their own song. The borrowee and the public then decide if the new tune is original enough.
If it's true that there is one general plot line, then there's bound to be similarities in stories. Writers bring the context of their entire lives to their stories, blending things that happened to them with things they heard others talk about either person to person or reader/watcher to writer/movie maker.
And now, we have ChatGPT who seems to have read quite a bit of everything everyone has written and with that context and the understanding of language has been able to create "original" stories. But for sure we know in this case that it is ALL borrowed and just rearranged in a unique way.
So on a continuum from totally unique to totally borrowed, there's probably a sweet spot where it's borrowed enough from general human experience to be relatable yet random/new enough to be surprising and entertaining. I hope your writings find this spot to your, and your readers' satisfaction!
Just my rambling thoughts inspired by your nice original Post. Have a nice day! :)
RE: How original do stories need to be?