ketchup, I've been there. Always got me mid November and I'd be able to cope again in early March - so I was interested if you had noticed a similar pattern in yourself.
Mine was a combination of situational childhood-caused anxiety. All of the things you have described, crying in the toilets at work, having no interest, feeling numb and disengaged, being anxious, a general feeling of dread... I used to have that every single winter. I used to talk to myself to get through the shopping, force myself to stay in the supermarket.
How it turned into the suicidal type of depression I think was getting so tired of the constant struggle to get through another day feeling like that. Heart thumping on the street, feeling outside of everything in company, not feeling safe. It became a terrible struggle to go through another day. I used to think if I could just make it to Christmas, the days would start getting longer and I'd see the end was in sight, but one year I just got worse. I just wanted it all to stop. I told my friend and DP and they brought me to the GP.
Medication was life changing. I was on Lexapro - this was prior to the availability of generics - and the GP said it was up to me whether to take them or not. My DP had booked a weekend in Paris around the 3rd week of January and I wanted to be well for that - naive view of magic pills! - but it gave me initiative. I also went for counselling and I remember thinking this is the first time anyone is actually going to help me. I was fine by March but GP advised me to stay on medication as he said there is a better chance of depression not reoccurring if you're on them for a lengthier time. I came off them the following March but needed them again in November. Kept that pattern for a few years. I never had any kind of side effects or withdrawal symtoms.
I'm not on any medication now. Looking back I know I was unhappy, but in denial about it, and able to cope during the summer months. But the lack of sunlight tipped me over the edge in winter.
And people who I told were amazed, as usually so strong, positive, cheerful etc.
Please go to your GP. I have no idea why I didn't go years before (I did try once but different GP said anyone would be upset by what I described and I failed to describe how upset I was). I wish I'd got help sooner. It would have saved me so much suffering.
for you.