It was like waking up and not knowing your own name, it was such a strange feeling to watch myself fuck up so badly, and be utterly incapable of stopping during the interview.

And I wasn't even particularly nervous about getting or not getting the offer either! They approached me, and I wasn't fully sure if I would even like the job yet!

I'm really glad that you and the parent posted these comments. As someone with pretty bad anxiety, this kind of thing prevents me from even going for interviews. And, unfortunately, after browsing this thread it seems that this possibility isn't even on most peoples' minds.

FizzBuzz-style filters not only don't prove that someone can code, they don't disprove it either. I'm not sure what the answer is.