It is a fabulous moment when our relationship with a work project changes from dreading the work and finding it exhausting, to enjoying the work and finding it refreshing.
If you are setting up a program of work that generates more positive reinforcement than negative reinforcement, then the work itself can often be refreshing. The work always takes energy, but if the relationship with the work is good, the energy you put is is typically matched by energy coming out of the work: work can feel good.
But this assumes that you are not overworking. Overworking creates negative reinforcement, making it harder to get back to work. I'm not saying there's no occasion that calls for 12-hour days or all nighters, but, especially at the front end of a project that you can anticipate lasting months into the future, there's also a very important place for developing a positive relationship with your work. Therefore, proper rest plays a crucial role in the development of a long-term constant practice.
(Yes, I was thinking of taking a night off from blogging. The preceding is a version of the reasoning I was using to justify the night off, but once I realized I could write about it, there was no longer a reason to take the day off.)