SAD is very real, and it can be a very real drag.
I can speak from the experience of having a SAD-like manifestation of my bipolar, which is that I am brutally affected by the sun at solstices and equinoxes. The winter solstice makes be blue, the summer solstice gets me high, and the equinoxes, with the amount of daylight sunlight changing so rapidly, leave me feeling agitated and unsettled for three weeks prior and post. Meh. Bipolar. You never know which wacky symptoms you'll draw from the grab bag.
I know plenty of folks from my other support groups who don't manifest bipolar but who do get hit with SAD. It's awfully hard to medicate, too, because by the time the meds have kicked in, the worst of it is typically over anyway. Some people get relief from light boxes, some from diet and exercise, some from ice cream or Pink Floyd. You never know.
No matter what you do, it's best you recognize it and see if you can't do something about it rather than to refuse to admit it and/or simply try to gut it out.
Good Luck.
BTW - my eyes used to be mostly green, and that's what everyone remembers them as, but since I've come clean with myself, everyone says they've turned grey. That's another clue to my chosen name.