Sun helps.  Or full-spectrum lighting.  My ex is bipolar and very affected by SAD during fall and winter.  I helped her obtain one during the rougher times and she claims it works a lot.  I know our brains get very dysfunctional for some during the dark months when we would be hibernating kind of in another era.

St. Johns' wort - studies have unfortunately shown it doesn't work as claimed.  But there is melatonin (studies are beaming at effectiveness), L-tryptophan (milk/turkey has them), lactic acid (essential for function - yogurt/cottage cheese have them too) - all good sleep and relaxation tools. 

Melatonin doesn't cause sleep - but says to brain - if it's dark I want you to go to sleep now.  So you take it a half hour before bed and make sure the room is very dark.  They found a gland behind the eyes that can catch some light/dark cues and seems to go along with melatonin.  In theory anyway that's why it works - melatonin cues it to put you to sleep when dark.  Jet lag causes the gland to not know what is what as the melatonin is too low after the trip.  Makes you think about it anyway.