> My supervisor told me I could stay home for a day, but if longer than that, I would require a doctor’s excuse.

You'd think the supervisor would realize it's in their own self-interest for you to not be around spreading infection (to them) by your mere presence.

There are of course people who abuse systems where doctors notes are not needed, and call in and then go have fun. It's not too hard to come across stories of people getting on short/long-term disability by know the correct doctor (I know of a situation where 3 members of the same family went to the same doctor and got a note for some condition).