Rawrnr, Dr. Bernarr Zovluck recommends complete rest while you are fasting. This makes sense to me, because if you are expending energy doing stuff, your body will not have spare energy to invoke a healing crisis. Here is a quote from his old website healself.org:

Fasting is physiological rest. Starvation is pathological. When you are not hungry, fasting is temporary abstinence from your ingestion of all food but drinking as much water as your thirst demands. When you are hungry, starvation is abstinence from your ingestion of food and water. Fasting exists until your body's surplus or stored fats are consumed and harmful accumulations are eliminated. Fasting is remedial, restorative and healthful. Starvation is denying your body essential food for its maintenance and is injurious to your body. When you fast, drink only water, lie down and close your eyes. Keep your eyes closed every moment of the 24 hours, every day that you water fast. During a water fast, you must have total physiological rest. You can only accomplish total physiological rest, by keeping your eyes closed. Feel, meditate, think on and concentrate on whatever are your symptoms until you are asymptomatic. Eat when you are asymptomatic, i.e., when you no longer have any symptoms or when you are genuinely hungry, i.e., when you are salivating for food.