Are my feet shrinking?

I think my feet are shrinking. No, seriously.

I've always been a size 11. Trust me, you don't just forget that you have feet that big, and no matter how much you may want to collect shoes, at that size, it's just not practical.

But, yesterday, when trying on an outfit I bought to show a friend, she lent me shoes to try with it. They're size 9 1/2, and they fit. I tried on the same pair at the shoe store today, thinking I might want to buy them (because otherwise I would need to return the outfit because I have no shoes that would fit). Same shoes, same size, and they were just too close for me to be comfortable. So, I'm thinking about it.

But, even if I did want to go a 1/2 size higher (which would be all that I would need), that would still be an entire size smaller than I'm using to buying.

Is this possible? Can your feet shrink?