When do you start bricking yourself on a Sunday night?

I work 4 on 4 off, days and nights, so any day could be a 'Sunday' for me, depends on when my shifts fall. As it happens, my first shift is tomorrow night, which is nice. I prefer working nights, so never feel at all worried about getting enough sleep or anything like that. When my first shift is days it is different, I know I should be sensible and go to bed early, but I rarely do and end up either having a couple of sleep or none at all, more frequently none at all. Not because of work, I don't mind my job and there isn't a huge amount of pressure on me, it is all about the waking up at 4am thing.