A trained physician will be able to distinguish these harmless symptoms from harmful symptoms that indicate the fast should be broken or a blood test checked quickly to make sure the fast is safe to continue. For example, a symptom such as dramatically increased weakness accompanied by a drop in blood pressure usually indicates the fast should not continue. Even though the signs which indicate that a fast may no longer be safe are exceedingly rare, the physician well trained in this modality must be able to assure the safety of all his patients. There is no reason anyone should risk a problem that may arise solely because they choose to do this on their own without sufficient education. A similar situation occurs during childbirth.
Most people understand that childbirth is a relatively safe and natural process.
Occasionally however, intervention by a trained professional is needed to optimize the outcome when signs might indicate a problem. The same is true for fasting. It is reasonable for an otherwise healthy individual to fast for two or three days without medical supervision when they have an acute illness and decreased appetite. This commonly occurs. Even then, if unusual symptoms develop such as vomiting, and there is the possibility of dehydration, medical intervention should be sought immediately.