My sleeping habits have been ridiculous for about 3 years now but I've managed to get up for work or lectures almost every time. I overslept once and was late for work (only time I've ever been late for work in any job) and I was 1 hour late to a 9am 2-hour lab practical last term and that's it.
But today I ridiculously managed to oversleep for a 10am seminar, I woke up at 10:20 because I turned my alarm off in my sleep. And then I thought, well I'm not going back to sleep now because I'm not rewarding myself for missing a seminar. But like an idiot I fell asleep again at 1pm and woke up at 3:30pm when I had a lecture at 3:00.
I've tried going to sleep before 12 but I always get back into old habits after a few days, I just have horrific self control/discipline. It doesn't help when halls people have loud parties/come home shouting at 4 or 5am when I'm trying to get into a pattern of sleeping at reasonable times. I actually wish I had something to get up for every single day because for normal school and most of sixth form I was hardly ever late and only skived lessons on purpose, never accidentally.
Just got to start being seriously strict with myself about when I go to sleep, I guess.