Productivity and energy level are corelated. I've a energy disorder problem, and it does have an impact (good and bad) on my productivity.
When your energy level is low, you feel lethargic, and it's very hard to get things done. When your energy level is high, you get so much done, sometimes even more than what you could do in a week/ month.
For me, I 'm not the consistent type. Look at this blog, you could see how it is. I stopped blogging for 10 months, and suddenly, this blog often has posts. I work on bursts of energy. When I'm bursting with energy for something, I would just keep working on it, and creating a lot of stuff. But this burst doesn't last indefinitely, after some time, it just wanes off, and I'm lethargic. To date, I have yet to be able to control this burst of productivity, as in...