I had my blood drawn and checked for vitamin D deficiency. It turned out that I almost had no vitamin D! I was put on prescription vitamin D for a few months and now take vitamin D every morning and evening. It has helped with fatigue, but has not totally removed it.

I totally understand, unfortunately! I joke around and say I should be studied because I go into what I call "hibernation". I am SO fatigued that I can sleep 18-24 hours without eating, drinking or going to the bathroom. It is like I am in a mini coma. I am extremely difficult to wake during these times. I call them my lost days. It is very weird. I have them after I've really over extended myself, if I am extremely stressed for several days in a row, or if I am sick. They do not happen daily or even weekly. But when they do happen, I don't know if it is fatigue or body shut down or what. But I understand your feeling. It is very depressing.

OMG, yes, I totally identify. And I think it's hard for people to grasp. I used to be very fit, gym was my health and social center. Until my weakened hand started dropping me off the TRX. In retrospect, I had been noticing tiredness some time before, but I could still work through it. Now--well, it's been three years of no gym, and even as I sit here telling myself I should go for a walk at least, my body says, "you're not up to that. At all." And of course, no one wants to be around inertia, so friends drift, since I'm never up for anything. Going to the movies once was a big deal. And more than one activity, like movie AND dinner? Can't do it. Yes, at this point fatigue is more limiting and isolating than anything else.

Absolutely. In fact, I use the same word, "constitutionally," as the fatigue encompasses more than "just" being tired.There's a whole constellation of awfulness.