I suffer from S.A.D too, mine kicks in at the end of July
End of July - blimey, that's bad! At least I can usually get to October before I really start to notice the change.
Hebden Bridge sits in steep-sided valleys so it can get very gloomy in the winter. Sometimes low cloud seems to blot out the sun for weeks at a time, especially since it barely climbs above the hill-tops when it is late in the year.
My S.A.D. isn't helped by the fact that I work from home in an attic room with one west-facing window which looks straight out at the nearby hillside. Bare trees, shadows and mud are all I see in the winter if I don't make the effort to go out during the day!
I hate the winter. I get some exercise every day, but being damp & cold just isn't the same. I also suffer from the cold, I seem to have a lower body temp than most people. Winter is just miserable
I'm not too bad with the cold. I haven't had to put any heating on since about April this year. I actually prefer it when we have a cold winter like last year because that often means clear blue skies, and snow on the ground reflects what light we get.
The ideal answer to our problems would be to spend winters in the southern hemisphere, or at least somewhere much nearer the equator! If I could afford to, I'd have at least a week off every month in the winter and take my bike somewhere sunnier like Tenerife.