I read this story a while ago, before 1990, probably quite a bit eartlier, and I suspect it is rather older than that (60s or 70s?). I think it was a short story, but I am not sure.
It is set in the future, and revolves around about six people who are on a tour of a factory or laboratory or similar. They are on a balcony or walkway, looking down on some device, the main exhibit of the tour. There is an explosion, the walkway collapses and they fall into the device (or its field). Most of the story takes place in the split second as they fall.
They find themselves in another world, and eventually realise this world is the product of one of the characters' imagination. Over the course of the story they visit a series of worlds, each one derived from the mind of a different character. I think the worlds are built from the character's subconscious, but the character can then control their world.
They escape a world when the character who controls it dies, and I think conclude they need to pass through all the character's worlds to get back to reality.
One world, from the mind of a middle-aged woman, seems nice at first, because she has banished all the bad things, but they realise she banishes too much, such as, I think, genitals! They (a man and a woman, the heroes of the story, I think) encourage her to banish more and more trivial annoyances, culminating in her banishing air, which kills her and so they escape her world.
The only other world I remember was that of a paranoid(?) man, who imagines cats that are inside-out because he so hates them.
Does this ring any bells with anyone? I had a search, but I do not think there are enough salient keywords to narrow it down.