Is Seasonal Affective Disorder actually normal ?

I live in Nova Scotia, Canada.  It is now getting dark by 5:30pm.  It is cold, 0 celcius or below.  There is snow falling outside.  Between November and February, the early darkness, cold temperatures and snow will continue.  We won’t see relief until April or May.

I’m not here to talk about the weather though. I am here to talk about how I FEEL in the weather, about Seasonal Affective Disorder.  I feel moody.  I feel irritable.  I don’t want to go outside (which for me is odd as I require nature to truly feel peaceful).  I am less able to handle the daily stressors that I was coping with effectively only a few weeks ago.  What is happening ?