Is fainting on Yom Kippur considered to be the type of illness which would justify breaking the fast? It would seem, that since there are many reasons why a person might faint, and it is not clear that fainting is directly related to fasting, that it would not be permitted to give the person food or drink until the reason for fainting is determined.
However, Hacham Ben Sion rules that since there is a doubt, he should be given food and/or water right away, even before receiving medical attention. Afterward, he shouldn’t continue to eat or drink, unless the medical professional determines that he should continue eating or drinking. Also, if the patient himself says that he needs to eat or drink, he may continue to eating or drinking.
Summary: Although though it is not clear whether a person who faints on Yom Kippur needs to eat or drink, he may eat or drink even before receiving medical attention.