I noticed this as well. When I was freelancing I would sometimes get inspired and motivated and work til 10pm or later, not because of a deadline but because I

I noticed this as well. When I was freelancing I would sometimes get inspired and motivated and work til 10pm or later, not because of a deadline but because I felt like it. Each time, I noticed the next day was rather slow. I was more tired and less inspired. Forcing myself to stop after 6pm worked wonders, I would wake up the next day easily, my brain overflowing with new ideas. On top of that I'd manage to sustain that motivation for several days or even weeks in a row.