You are not separate from Nature, you are Nature. And Nature follows a cyclical lifestyle. And you are no different. Capitalism expects humans to continue to pour out the same level of work all year round. This is unsustainable. You do not expect a tree to produce leaves during the winter. You should not expect the same for yourself.
I do not believe there is such thing as 'Seasonal Affective Disorder': a 'disorder' characterised as a period of low moods during the winter. It is not a disorder, and please do not listen to doctors if they say you have this. What you are experiencing is your body naturally fighting back against your constant pressure to continuously work during a period in which you are supposed to be resting. This will naturally cause you incredible strain that will leave you physically and mentally unwell.
There is nothing wrong with you if you have been told you have 'Seasonal Affective Disorder'. There is something wrong with the culture in which you live. Please know this. It will take off a tremendous amount of pressure from you and allow you to be kind to yourself as the seasons begin to change.
Now, until this becomes more widely accepted, it may be difficult for you to find the rest you need - however it is not impossible.
It is your job to remind yourself during the winter period that this is a time for rest and recuperation. It is a time for looking within and simply Being. You should not be expecting yourself to give the same level of work as you do during the spring and the summer. Humans are not machines.
As this winter time comes, please give yourself rest. Make that your priority. Speak to your managers and make sure you do not take on any new big projects from this point forwards, let them go to someone else. Take mental health days. Spend your evenings and weekends resting and giving yourself permission to rest. The capitalist mindset may make you feel uneasy with this at first. If so, again, look at the trees dropping their leaves as they ready themselves for the cold. Look at the squirrels storing their foods and snuggling up in their homes for winter. Look at the bears cosying up in their caves readying themselves for their slumber. Look at the birds escaping the cold to rest in the warmth as they make their way south.
Humans must take their same precautions. There is a reason why human suicide rates go up during the winter. It is not just lack of sunlight as many doctors suggest. Vitamin D supplements and light exposure can be beneficial, of course. But this is not the primary cause of the rising suicide rates in the winter. It is the overworking and high levels of pressure during a time that is supposed to be dedicated to rest. Give yourself that rest, and do not feel bad about it. It is the most natural thing in the world.
Please share this with your friends and family as the seasons begin to change. I feel if more people knew this, a lot more people would make it through the winter unharmed