The closest equivalent to that kind of synesthesia I can think of in my own head is the disorientation I sometimes experience when trying hard to communicate with someone whose expressed beliefs are absurdly disjoint from mine.

That is, not when they disagree, but when I haven't (yet) understood them well enough to disagree, where what they say doesn't seem to connect to reality enough to even be false.

That can be a delightful feeling when it's a single absurd thought in the context of an otherwise coherent relationship, admittedly, much like how roller coasters can be fun, even though the same physical experiences on a train would be traumatizingly terrifying. (I also enjoy absurdist art in the same spirit.)

As I say, I often experience that as a kind of physical disorientation, similar to vertigo. I classify this as a self-induced hallucination, rather than any kind of perception... that is, I think I could train myself out of it and not lose any data in the process.