I am sorry to hear about the brain fog problem when fasting. I can give you my two cents, but I'm far from an expert.
First, let me tell you of an experience I had. About one and a half years ago I went on a nine day water fast. During this time I started getting pain in an old injury that happened about fifteen years ago. I had torn some tissue in my lower back when I twisted myself. I know it was a dumb thing to do. It took me several years to get over it. Yes, I felt the pain for years. Now I had been over it for years. During this fast from one and a half years ago some of that pain came back. Of course, it wasn't anything like when it happen, but bad enough to be uncomfortable. This time it took me several months to get over it. My theory is that while I was on the
Water Fast my body was doing some healing in the area of the old injury. I think that if I could have stayed on that fast long enough the body would have completed its work and I would not have had the issue for several more months.
My theory about your brain fog is that your body was doing some healing on your brain since you have had brain lesions in the past. It did not get a chance to finish the healing process before you broke the fast so it took some time to calm down after the fast, thus the brain fog.
I wonder what the outcome would have been if you would have continued the fast on water only for several days when you broke the dry fast. Of course, there is no way of knowing how long your body would need to fast to cure it completely. You may have to do several fasts to cure it. If you did decide to do this you would definitely need to arrange for complete down time from your cares of life not only during the fast, but for some time after the fast as you do not know at this point the outcome or how long it would take you to recover.
Also, each fast is different. I was expecting my next nine day fast to cause that old injury to be stirred up again, but it never happened. I guess my body, in its wisdom, was working on other things. You may not have the brain fog experience each time you fast.
I'm glad you mentioned your interest in dry fasting for spiritual reasons. This is also the main reason I want to eventually step out and dry fast. I know that
Water Fasting can bring powerful spiritual benefits. Since dry fasting is more effective than
Water Fasting for health, I am thinking that this may also be the case in the spiritual realm.
I recently listened to Derek Prince speak on fasting for spiritual benefits. He said it is dangerous to dry fast more that 72 hours, but many have proved him wrong on that account. I guess it could be dangerous if a person did not do it right and did not listen to their body. What I found interesting about his talk is that he said he did know a preacher named Tommy Hicks who turned Argentina upside down some considerable time ago. This happened after he did a 17 day dry fast! That makes me think dry fasting for spiritual reasons is more powerful than water fasting.
Seventeen days is really pushing a dry fast to the limit and then some. We don't know, he may have been supernaturally sustained by God during this time. I definitely don't think the average person should jump into a 17 day dry fast as death may follow. I'll leave you the links in case you are interested in listening to Derek.
http://www.youtube.com/watch?v=9GS2pfhfeVc
http://www.youtube.com/watch?v=0oxqZoblkAg