I find the same sort of result with coding on little sleep. While it feels like I'm "high functioning" while coding at 4:00AM, a code review in the light of day after a good night's sleep often reveals that I wasn't.
I've begun to suspect this is because we don't notice all the little issues we'd notice if we were more awake - at 4AM, the code is Flying, because I'm not stopping to realize how crappy the code is.
I've had similar experiences. If I am very tired I don't get "coder's block", but the code is often rubbish.