I've never missed much other than course lectures from oversleeping, which is no biggie as I "planned" to miss it since if I knew I didn't need that lecture/could read the presentation materials and learn it on my own.
However, one case last semester, I was finishing up a midterm group project and a presentation to be given the next morning. My part of the presentation was rather important since it was the core of the project, but I had overslept and missed a couple shuttles to campus. So I got to the class with about 10 minutes left in it. :/ My group just finished, and they couldn't discuss my part in detail since they had no idea how I did what I did. ;_;
Fortunately, the professor was cool and let me present the following week with a slight deduction. Good thing too since it was definitely the most kickass project of all the groups.
Jam it back in, in the dark.