I suffer from SAD as well. My heart goes out to you.

Everyone has already made great suggestions. The only thing I could add is...

Exercise definitely healthy and tires me out... but it is so outlandish to consider when I get winded from walking across the room, and I don't even have energy to chew my food.

When this is the case, I try to do stretches (Yoga-style) in front of the TV. Or do some meditating/breathing exercises to relax. It makes me feel like I'm doing something to ease my anxiety and stress without over doing it.

I hope you can find what works for you.