Just because I'm staring off into space doesn't mean that I'm enjoying mental downtime. I'm hard at work here mister. In fact, some of the best creative times for me happen when I examine those empty spaces that exist between all the 'doing'. It's in that silence that sometimes I can hear most clearly.
Dreaming out loud, inspiration and problem solving can happen at a moment's notice. It can even hit you in the shower. For me it often comes while I'm on a morning walk with Domino, my Jack Russel Terrier. I have no trouble putting my mind to bed and getting a good night of sleep. It's all these waking hours that exhaust my brain.