" Bob,” I said, louder. “Are you saying it… it ate my magic?”
Bob got a defensive look on his face. “Not all of it. I woke you up as quick as I could. Harry, don’t worry about it, you’ll heal. Sure, you might be down for a couple of months. Or, um, years. Well, decades, possibly, but that’s only a very outside chance—”
I cut him off with a slash of my hand. “He ate part of my power,” I said. “Does that mean that the Nightmare is stronger?”
“Well, naturally, Harry. You are what you eat.”
“Dammit,” I snarled, pressing one hand against my forehead. “Okay, okay. We’ve really got to find this thing now.” I started pacing back and forth. “If it’s using my power, it makes me responsible for what it does with it.”
Bob scoffed. “Harry, that’s irrational.”
I shot him a look. “That doesn’t make it any less true,” I snapped.
“Okay,” Bob said, meekly. “We have now left Reason and Sanity Junction. Next stop, Looneyville. "

― Jim Butcher , Grave Peril (The Dresden Files, #3)