Basically, these questions are "icebreakers". It's a good "bridge" mechanism. You're right that you can't really jump in and say "hey teacher, guess what, I've got depression!" that is way too abrupt. But, if you can come up with "middle-ground" questions, that's good. When you say "Do you have some time? I need to talk to someone" that already sets the scene. He knows something is up and gives him time to prepare too, like keeprolling said. So, if you can think of any questions like these, you will easily be able to reach out and make the whole process much simpler.