Disregard the previous answers if you fast for more than 24 hours. If it's 24 hours or less, then I wouldn't worry.
If it's 24+ hours, then electrolyte depletion becomes a consideration. Our brains need sodium, potassium, and manganese to operate. Everything we eat contains these elements so normally we needn't think about them. However; if you fast for more than a day you might want to consider them.
Table salt is everywhere. Add a little to something and you'll probably get enough. Disregard anything you've ever read about salt. If you crave it, your body is telling you that you need more.
Potassium exists in all of our foods as well, but when fasting we may not be meeting our bodies' demands. Potassium acts with sodium as it's opposite end. They react one-to-one and we need equal parts for our brain chemistry. Cream of tartar is an excellent source of potassium. It is potassium bitartrate. A quarter teaspon of this should be more than enough per day (but do your own research, don't believe what you read on a forum without cross-checking purported, 'facts')
As for your manganese, add a little apple cider vinegar to your diet. I'm not associated with the following link, but I've done a little research myself and I think this link might be helpful.