"If it works... it is to magic use, what resting is to being able to run longer. And as for the potential downsides... you may find it a bit difficult to fall asleep easily for a while longer, lest I pull some of that energy back from you, or you work it off yourself. Like... Oh, what was it called...." She made a face, trying to remember. "Coffee? Except it doesn't have a taste of its own, exactly...."