I have never told someone about this, but the opposite happened to me. I had been tested because I was different than any other child of my age. And was diagnosed with a very high IQ (you can guess how many friends I had), but after I was attacked and hit heavily at my head by some russians without a reason (for their pleasure), I have lost most of my ability to think as fast as before. I was in coma for 2days at the local hospital and have no memory of what happened, except of what friends told me. I can't explain how life depressing that was for me, but almost 7y later, I started to gain a little in my speed of thought. However I'll probably never be that smart again and it feels like a big loss to me. I'm still quite talented, but nothing comparable to before the attack.