Have you considered that you may be suffering from dehydration and possible borderline malnutrition, not to mention wildly fluctuating blood sugar? For me, for some unknown reason, SLE has totally killed my appetite and desire to eat even my most favorite foods. It's a very real feeling that nothing sounds appetizing, and nothing tastes good at all. I have to literally force myself sometimes to put a fair amount of food on my plate and eat it all. Eating is often times a chore. If I give in and skip meals, or eat just small amounts, I get bad diarrhea, awful fatigue, dizzy spells, and my moods swing to extremes from the fluctuating blood sugar.
I don't take any antidepressants, so I'm not sure if that could be part of your problem. I have no idea why my ability to enjoy food has left me over the past few years, but it is a common thing many people here talk about as a symptom/problem with SLE. 20 hours without food is way too long. And diarrhea will cause dehydration very quickly, making matters even worse. I wish I had a reason and solid answer for you. Your symptoms are very much like mine, but I have no idea why I have no appetite anymore, or why you are having a bit of the same, other than it's something many people with SLE deal with.
You will definitely get more responses from this thread than you will from the blog. I suggest you check back frequently to see what others have to say. We have a fair amount of collective experience here, so someone may have a better answer and explanation for you.