I respect what hopsinso is saying, based upon their own experience. However, fainting is not *always* a sign for concern, as people (including me) have fainted for reasons as simple as being too warm in a stuffy room, or standing up too fast. And indeed, if someone is fasting, not getting enough water and becomes dehydrated, that *can* cause them to faint.
More medical facts on fainting at the links below: