Visiting the house I grew up in this past holiday season, I had the strangest experience. I found my old notebooks from when I was about 14...and couldn't understand the contents!
I had been a math prodigy, entering college when I was 13. But, after a couple of years as a good college student left for social reasons to become a pretty mediocre high school student. Over time, I ended up focusing on other things and the math skills deteriorated.