Not the person you asked, but as someone who also cannot see mental images at all I'm not entirely sure what you mean by "imagines sex". I don't really imagine sex and self-gratification is usually not worth it without visual aids. The times I pull from memory, it's more about the overall experience rather than visualizing anything specific.

As far as math goes, I've always been pretty good at it. I generally don't think about graphs at all in mathematics. That's something I associate with learning math more than I associate it with "doing math". The only time I'm reaching for more complicated math is in a computer science context so I'm rarely trying to solve anything other than arithmetic or rough approximations in my head.