Working on a problem late can sometimes be beneficial. I've been up late with a problem in my head and went to bed with little downtime. It's hard to go to sleep, definitely. However, I've actually dreamt the solution a few times, and woke up the next morning knowing exactly what to code.

This happened two nights ago. I was coding something fairly complex and had a hard time connecting everything together. It was something I had been struggling with for two weeks. In a dream, I figured out how to make things much simpler. The next morning I deleted 1000 lines of code, re-structured things, and got it working succinctly.

But you definitely don't sleep very well when you do it. :)