I had a recurring abstract nightmare as a small kid (don't think it was related to fever but I guess those were pretty common) which was basically about a line, gradually becoming messier and messier until it was all just a big jumble. I could never explain it to anyone else, but it terrified me for a time.
Crazy, I used to have the exact same (well, as best as I could describe them they were the same) dreams. I can still vividly remember the feeling of them, of the perfection of the line, and the growing pressure of some external force trying to mess it up, until eventually it always did.
I'm wondering if "geometric nightmares" is a reoccurring dream I've had since I was a kid too, basically two cog-wheels linked with each other, but one is extremely huge and the other unbelievable tiny. I'd never describe this as a "geometric nightmares" though, but it does kind of sound similar.
Maybe there is something about "contrasts" as they all seem to be vaguely related to "big difference" basically.
I've heard these fever dreams referred to as big-small as well. I believe it's the same phenomenon. For me it was pillars from high up above, where they're all the same width, but one is also much bigger at the same time. Hard to explain... Just an odd feeling.
And, anecdotally, I have gotten a similar feeling reaching deep enough meditation.
