I've seen this phenomenon quite a few times, usually with people who had survived really massive brain injury. A bus driver was suddenly genius level in math, a little old man suddenly started to speak Portuguese when he couldn't get a single word of English out. In the latter case, his family recalled that grandparents had spoken it but that no one else in the family had.
No, you haven't - unless what you mean by 'seen' is 'on television', 'in books', or 'read on DU' - The odds of someone ending up with an increased ability because of a traumatic brain injury are slim to none.
I think you have read too many comic books. In the real world, traumatic accidents do not make superheros.
Edit:
I read the linked article - There are about 30 known cases of this phenomenon. And Warpy knows 'quite a few' ?
She must be the TiT of brain damage.