text: Sunlight.  I naturally wake up at sunrise, whatever time that is.  When I try to override that and set an alarm to force myself to get up in the dark, it makes me feel fatigued, stressed, and irritable all day.  Now that I run my own business and can set my own hours, I have stopped trying to override my body's natural response to daylight and seasons, and now just plan for it and go with it.  The result is that I am MUCH happier, healthier, and calmer person.