You are right, it was a Supersaver tickets, but the principle was the same. They told us to bring a medical certificate, (but since it would be a week after the date,..and by then the person would be feel much better to travel anyway..) it wouldn’t make sense to get the certificate a week later anyway. I contacted SBB twice by email, but they didn’t seem very interested in helping or understanding. Anyway, thank you for your suggestion.