DP has it every year. He's usually (his description) 'going a bit weird' by late September.
So we're hitting it head on this year to see if that helps.
A-Z Vitamin daily. Extra vitamin D daily (I have huge deficiencies, as my pasty as fuck Scots heritage skin means I can't spend time out in the sun.
Sunrise clock, with the sunset function used at night.
Forcible getting up and out every day, without fail. Curtains open and windows open from first thing. Walk outside at lunchbreak, without fail - even when it's raining, get an umbrella and get outside, as the daylight, even on a crappy day, is still daylight.
Masses of veggies at every meal.
Activity. Not flumping around on the sofa until 'things' are done, whether that's housework or something more enjoyable.
And the soft, squishy, cozy stuff as well. Lots of lights, comfortable furnishings, comfortable clothes and shoes, as it's a whole load harder to feel happy when your socks are wet and there's a cold draught down the back of your neck.
So far, he's been completely different this year compared to others.