Netherlands though, not the US. If they're anything like most of Europe then a doctors note is all you need to still be paid while sick more than 1-2 days.
But how about if you run the business on your own, and you're concerned that if you take two weeks off the business will lose many customers who won't come back?
(I was shocked when I saw the they put the name of the illness on the note. That's so far from my employers business that it should be illegal to even ask. Employees and consumers rights in Germany seem to be seriously limited.)
You get multiple papers in Germany. The one without (!) diagnosis is for your employer.
As an employee the employer will have insurance but basically have to eat the cost of short sickness.
I'm a freelancer but I've chosen not to buy the insurance. It's very expensive and can survive on her income. I put the money I would have spent into a buffer.