SAD, not sure, but I do/have suffered from persistant low mood, I suppose it could be termed a depression of sorts, although I don't think you can use the term without taking each individual on their own merit. Emotional instability yes, feelings of sadness etc, definately made worse by erratic sleep, and anxiety increases significantly if I stay up late and wake up late, dropping to small amounts with a stabilised sleep/wake routine. I think it may be an accumulative thing? We are talking years of dysfunctional rhythm that may become chronic with stress dumped on top? My EA began during high stress, and where my sleep was worst.
For me now in bed before 9:30 and rise around 7pm. Trying to rise with the sun and have eaten my last meal within 2 hours of sunset. Obviously as the day lengths increase into the summer months circadian rhythm could be adjusted accordingly? Try a piece of software called f.lux which helps filter out blue light from screens, which we don't want during the evenings. Give it two weeks minimum.. hope this may help.