I’ve also been struggling with dizzy spells while fasting. It could be low blood sugar, electrolyte imbalance, or dehydration. I think mine is blood sugar related, because I do take electrolytes. I fast for 38-42 hours 3 days a week. If I’m feeling dizzy and water/electrolytes hasn’t solved the issue, I will eat a small portion of food. That usually solves it. I’ve found that listening to your body is just as important as fasting, so don’t be afraid to eat more during your eating window if your body is asking for more!