Spare Parts for the Mind
Novella 20,225 words Recommended by 3 award/anthology sources
"He supposed he must have been daydreaming, but whatever pleasant distraction had occupied his thoughts a moment before, it was gone now. In fact, he could not recall the state of mind from which his mind had wandered, though he must have been paying attention to his surroundings at some point..."
Quasar links out; the story lives on Asimov's, where the author gets the click.