Does anyone else experience this?

I am finding lately that my depression has reared its ugly head, and every effort to move is countered by an equal and opposite push of lethargy. Even when I work past it, getting my butt on that elliptical runner and pushing past the 20 minute mark, I am so mentally/physically wiped out that I need a nap right afterwards.

This doesn't seem normal to me. Shouldn't I be energized? I used to get a slight mental boost from pushing myself.

I wonder if it's the winter. It's been awfully cold and snowy around here lately.

I used to deal with a similar issue. Remember to take a Vit. D supplement in the winter. Many nutritionists don't agree that the recommended 400 IUs is nearly enough. I have to say that I agree through my own experience. 15 min of direct sunlight is enough to produce 1000 IUs so you can certainly take more.
Scrutinize your diet to make sure you are getting enough iron.
But the BIG THING with me and my (gone) fatigue was loss of muscle mass- which I thought may have been depression or low thyroid after losing 60 pounds.
So the question is... are you in a calorie deficit?
Being in a calorie deficit (i.e. losing weight) means that your body will take those missing calories for normal maintenance from A. Glycogen stored in liver, B. Body fat and C. MUSCLE.
After glycogen stores, do you know which one your body will preferentially catabolize?
It's NOT body fat. It's muscle mass. And I don't mean the result of natural atrophy do to losing weight. It's actively and preferentially being catabolized for energy when you are in a calorie deficit.
Resistance training made me feel so much less lethargic after only 2 weeks because it rebuilt the muscle and kept my body from using it as energy. Now I can WALK! And it doesn't feel like moving a mountain to take a damn step! Try it. And don't use those silly 3 pound weights either. Start with some basic weight lifting moves and lift the heaviest you can manage. That means, don't touch that 5 pound dumbbell!

But otherwise, yes, physical exercise definitely makes me want a nap.

Another issue that I faced, that I think is related, is that your mind will try and fight you every step of the way when you are trying to make a change. Part of you desperately wants to stay the same because it is so comfortable. You just have to keep trying and keep pushing!

Luckily we're here to help each other when things get hard

If you find exercise does not rejuvenate then you it is surely depression (if its not a physical disorder) and you are better off not pushing yourself and resting yourself instead.

If you push yourself and find you feel rejuvenated then by all means that's what's needed. Often enough depression just turns into lethargy and we miss the moment to push ourselves.

As to vitamin or mineral deficiencies, only a doctors tests can really tell you if they are an issue. And it can be harmful to take more iron or other substances because you think they might be an issue. People always seem to be in a hurry to think they've got some vitamin deficiency or metabolic problem.

If you've got SAD then get one of those lamps if you think they will help.

so back to depression and fatigue, try to find ways to lift your mood. Be patient. Do it through nurturing self talk. Be gentle with yourself but try to avoid sabotaging self-indulgence i.e. chocolate and stuff like that. Take it moment by moment. find little ways to keep your spirits up. And get the rest you need.

As to the food, check your maintenance calories and just eat accordingly until you are feeling more motivated and optimistic. That way at least you might be able to avoid boredom eating or bad food habits. if you know what i mean.