Why do we feel weakness when we start fasting?
It is completely normal to experience a little weakness in the beginning of your healing journey. It's a sign that your body is detoxing & healing itself.
When you start following the Satvic lifestyle your body starts eliminating the waste and toxins accumulated inside.
During this time all your Pranshakti or energy is occupied in cleansing and healing the body. Thus, you may feel weak.
Along with 16 hour fasting, make sure you also follow the rest of the steps (Satvic food plan, wet packs, enema, sunbathing, exercise & pranayama) as they will help you accelerate the healing process 10 times.