I have been challenged on this question recently because I've been taking on many, many projects. I check my email as soon as I turn off my alarm when I wake up in the morning, I turn on my computer in between making the morning coffee, I pull out my phone to check notifications over and over, and I work on several projects each day (and am learning over and over again how terrible I am at time management).
So the basic point of this post is, be honest with yourself about how well you practice rest, and recognize that the simple truth is that establishing a rhythm of rest is actually crucial to long-term productivity, drive, and creative inspiration. If you find yourself unable to practice rest it may be that you don't actually believe what I just wrote about a rhythm of rest, since our deepest beliefs are generally revealed by our habits and practices. This means you may need to spend some time refocusing on what rest is and why it's so significant. If you follow Jesus, keep in mind that he is recorded as regularly resting; and of course God himself instilled rest into the very fabric of human work, which seems pretty important.