I'm right there with you...for the past 2 days. Out of NOWHERE. Today is worse than yesterday. Yesterday, I just felt tired/sleepy at work but I was still able to function. Today at work, I can barely keep my head up and I can't concentrate. I went home at lunch and napped for an hour.
If I had to guess, my Iron levels have gotten low again. I'm going to have to consider an iron infusion as I've now (after experimenting for the past couple of months) determined that Ferrous Sulfate, in any mg, causes me great stomach pain...to the point I can't each and drop weight within days.
I also agree that fatigue might also having nothing to do with Iron levels being off...I think it just hits when it wants to with this disease. It sucks. It's the one thing (besides the actual intestinal flares) that really makes me feel like crap.