Thought I might add, for the first time in 16 years, I took enough sick days in a row to warrant a medical certificate. I didn't know what it was so I went to a random GP. She was perplexed so she tested for a bacterial infection before deciding if I needed antibiotics or not, then she asks if I need a medical certificate, how much sick leave I have, and if I wanted a week off. Not gonna say no to that and I think I'll keep her as my new GP as my last one retired. Ended up being the world's weirdest flu.
I'm always baffled when people in other countries explain what hoops they have to jump trough to stay at home when they are ill.
Here you just call in and say "I'm ill, I'll let you know when I'm back" and that's it.
If it takes a long time. i.e. longer than two weeks orso, meaning you've got something worse than the flu you get an invite to talk to a doctor which will be assigned by a special health agency (@Quark is that the right term? ) and from there on they will handle it.
Of course you go to your own doctor to get all the medical help you need, but you don't need any proof from them to call in sick.