I've found my poor sleep correlates with how late I'm working on a problem. I try to go to bed around 11pm. If I'm done working by 6pm I'm more likely to sleep ok. 8pm is pushing it. Any later than that the problem won't be out of my head by the time I lay down, and it stays there all night.
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. :)
