I've always had managers who care more about what I deliver than when and where my butt is in a chair. Maybe I'm lucky, maybe I'm good enough that it works out that way.

No, I mean, that’s perfectly acceptable. If your boss cares only that you deliver, and doesn’t notice/care that you are gone for a few days due to sickness, that’s still not on you.

Have you considered just informally notifying them that you're out because sick? I mean, not doing that is fine too if you can deliver, but informing them might build more trust.