I suspect that you and JoshuaZ are unpacking the phrase "Old Testament miracles" differently. Specifically, I suspect they are thinking of events on the order of dividing the Red Sea to allow refugees to pass and then drowning their pursuers behind them.

Such events, when they occur, are not personal experiences that must be shared, but rather world-shaking events that by their nature are shared.

And don't be too hasty to dismiss millions of personal experiences as mental illness.

First of all, Joshua didn't bring up mental illness here. But since you do: how hasty is "too" hasty? To say that differently: in a community of a billion people, roughly how many hallucinations ought I expect that community to experience in a year?