I have the bad habit of skipping classes when things get rough, too. :|Right now, I've already skipped school today and yesterday, as well as several days last week. i have two tests that i was supposed to do today, both i am unprepared for, as well as an assignment for another class due friday, and a proposal for another class due yesterday. I also have this extracurricular thing that i signed up for (in a brief moment of confidence) that i have been avoiding even though I'm actually needed in it. I am so stressed and overwhelmed right now, and obviously, doing my usual thing of skipping school to avoid it.
I have done this so many times before. How can I avoid it (ha...) in the future? As, in, things to do..
Do your professors know about your anxiety? This probably sounds really scary, but it might be a good idea to set up appointments with your teachers at the beginning of each semester and talk to them about having SAD. By telling them that class can be a struggle for you before classes really get started, most of them will be more understanding if probelms arise in the future, where as if you talk to them when the problem comes up (like during midterms or something), they may be less inclined to believe you.
I wonder if there's a way you can get documentation for SAD. Some school health centers might have a program or test that can prove you have a real condition, so that even if a teacher doesn't care about it, they have to take it into account anyway. I've done it for my learning disabilities before, but I don't know if you can do the same thing for SAD or not.
As far as what you can do right now, maybe try emailing your teachers and the extracurricular thing you have? Perhaps try to explain that you've been having some problems, and ask what you can do to make it up?
I hope it gets easier for you. Class can be brutal.