How Do People Discover They Are Mediums?

Just as it asks in the title. Does it happen suddenly or slowly over time? Do all mediums or clairvoyants have a similar story?

I can quote the following case.
My grandfather had a farm and he needed a new well drilled to supply more water to the cultivations he was planning.
He went to a dowser who, needless to say, found not one but three good spots to drill an irrigation well.
When inquired on how he discovered this "gift" he told the following story.
After entering puberty he noticed that each time he was crossing a particular square to attend church he felt "strange". Initially he just felt a trifle queasy but as the years went on he began to feel violently ill, to the point he needed to take an alternative rout to church. Traditional medicine could not help so he turned to a Capuchin monk (as I've already said in Catholic countries they are widely believed to be have lot of "occult" knowledge) for help.
This monk quickly discovered the nature of his "illness": under the square a number of deep wells were drilled in the past and then paved over when they weren't needed anymore. He also taught him how to "control" his gift and find deep-running water.
He didn't use a divining rod as usually pictured: he just walked over an area and when he started to feel "strange" he marked the location, double checking it later.
I have no explanation to give, except that... it worked!

My friend from the 'What Do Psychics See' topic started seeing things on a regular basis when he was about 16, just after his parents split up. They do remember having strange experiences earlier including two out of body type experiences when they were really quite ill. I think I am right in saying that a pair disembodied legs appearing in the sixth form common room was probably the start of it. They were described as a rather detailed grey apparition. My friend was terrified, falling back and scurrying off across the floor away from them whilst everyone else in the room just watched them make a fool of themselves.