Most Helpful Guy
At university, in Belgium, generally attending courses is not mandatory, except for some language courses.
But if you want to be certain ask for a doctor's note and make sure you have it with you to prove where you were :D
Generally it's best to ask the secrateriat at university if it's a common practice to bring a doctor's note!1
Most Helpful Girl
Depends on the University or Professor. It's really up to you to show proof if they don't believe you.
I had two Professor's who wouldn't accept doctor's note. I was in the hospital for a week and the day I got out we had a test. The Professor still had me take the test and wouldn't take my assignment due the week before when I was admitted to the hospital. I had the doctors note and everything.1