It's not insane - your body, your choices. I certainly wouldn't be offended if you asked although I may not have ones as current as you'd like and probably wouldn't go get new ones JUST for a single casual encounter. Were we beginning an ongoing relationship? sure, that's fine.
That said, I'd really spend some time working through *why* you have such a fear and whether that level of fear is reasonable compared to the level of risk. Like, take herpes. Two main forms, right, HSV1 and HSV2 - the latter mostly likes genitals, the former mostly likes mouths, oral sex can throw those "mostly" descriptors out the window. And everyone acts like they're a big bad huge thing - "oh no, you'll have this forever". Truth. And yet... they don't point out that something like 30-40% of people have HSV1, most don't know, many many (myself included!) got it from family as a child, and that - unless you're otherwise immunocompromised OR are newly infected during pregnancy, there really aren't any health issues caused by it. The whole stigma was literally a scheme by big Pharma to sell more Valtrex (
This article on Vice is the easiest one for me to pull offhand but there are LOTS out there).
HSV2 can be worse but again for most people, after the initial infection, is a non issue *other than the stigma*. HPV? get the vaccine, that will basically keep it from giving you cancer, and after that it's a minor skin condition that can be managed if you pick it up (not to mention the body often clears that one up with no symptoms).
You're by far not alone in having these fears - we're spoon-fed the idea that sex, especially casual sex, is deadly or harmful from the time we're teenagers. (If you can't scare the kids with hell, scare them with deadly diseases or at least stigmatized ones...) The reality of these things is NOT that though.
Just something to think about...