In ordinary conversation, only one has the same meaning as one and only one. The shorter phrase is used almost every situation. In mathematical logic, it's often desirable to make a distinction between zero or one and exactly one. In that situation one and only one is used to indicate that the count cannot be less than one or more than one.
Yes, the person would yell once you fell, but only if you fell. "If" and "Only if" used in the same way means the same thing, except that "only if" is more forceful, more compelling. "If and only if" is the most obligatory of the three, in which the action has been distinguished and emphasised, "If, and only if " It's the most forceful of the three