I know it is real for me (however "they" want to classify it is fine by me).

By the middle of October I can feel it coming on and it doesn't let up until the beginning of April. And I live further South than I used to so I can only try to remember how miserable I was when I was living in the Northeast as well. (I don't remember much from that time so I think that says it all.)

Even sunshine while it helps doesn't help kick it - sometimes I embrace the rainy and cloudy days - let myself roll around in the depression and sometimes that helps. Sometimes it doesn't.

I have found things that help me manage it (getting outside for 20 minutes, eating three meals a day with lots of fruit and veggies, drinking at least 6 glasses of water, writing/journaling, watching funny TV shows, writing) and just expecting much less of myself for these months.

It's not something I can fix or change and luckily I have a patient partner who understands and helps with seeing what is going on and when I'm being destructive. It's definitely real though - and taken me 9 years to realize it!

Best wishes to you as you find your way - it can be tough but you will find things that help alleviate it if not lift it completely.