[smokinn]

That's completely untrue. I'm the same as the gp. When I don't have a rigid schedule I absolutely have to follow (whenever I'm unemployed or when I was in school) I drift around the clock. It's much more natural for me and I feel much more rested than when I'm on a fixed schedule.

[gte910h]

Most people have this issue, some to a larger degree than others, if they don't give themselves strong light cues.